A committee (or "commission") is a type of small deliberative assembly that is usually intended to remain subordinate to another, larger deliberative assembly—which when organized so that action on committee requires a vote by all its entitled members, is called the "Committee of the Whole". Committees often serve several different functions:
Governance: in organizations considered too large for all the members to participate in decisions affecting the organization as a whole, a committee (such as a Board of Directors or "Executive Committee") is given the power to make decisions, spend money, or take actions. Some or all such powers may be limited or effectively unlimited. For example of the later case, the Board of directors can frequently enter into binding contracts and make decisions which once taken or made, cannot be taken back or undone under the law.
Coordination: individuals from different parts of an organization (for example, all senior vice presidents) might meet regularly to discuss developments in their areas, review projects that cut across organizational boundaries, talk about future options, etc. Where there is a large committee, it is common to have smaller committees with more specialized functions - for example, Boards of Directors of large corporations typically have an (ongoing) audit committee, finance committee, compensation committee, etc. Large academic conferences are usually organized by a co-ordinating committee drawn from the relevant professional body.
Research and recommendations: committees are often formed to do research and make recommendations on a potential or planned project or change. For example, an organization considering a major capital investment might create a temporary working committee of several people to review options and make recommendations to upper management or the Board of Directors. Such committees are typically dissolved after issuing recommendations (often in the form of a final report).
Tabling: as a means of public relations by sending sensitive, inconvenient, or irrelevant matters to committees, organizations may bypass, stall, or disacknowledge matters without declaring a formal policy of inaction or indifference.
It is common for a chairperson to organize a committee meeting through an agenda, which is usually distributed in advance.
The chairperson is responsible for running meetings: keeping the discussion on the appropriate subject, recognizing members (calling on them to speak) [often omitted in smaller committees], and calling for votes after a debate has taken place [formal voting is normally only done in committees involved in governance]. Governance committees often have formal processes (for example, they might follow Roberts Rules of Order); other types of committees typically operate informally, with the chairperson being responsible for deciding how formal the committee processes will be.
Minutes, a record of the discussion and decisions of the meeting, are often taken by a person designated as the secretary of the committee; they may be legally obligatory (again, typically for governance committees, especially boards of directors).
For committees that meet regularly, the minutes of the most recent meeting are often circulated to committee members before the next meeting, and are available to the membership of the whole.
Committees may meet on a regular basis, often weekly or yearly, or meetings may be called irregularly as the need arises. During an emergency, a committee may meet more than once per day, or sit in permanent session, as, for example, ExComm (the President's Executive Committee) did during the Cuban Missile Crisis.
A committee that is a subset of a larger committee is called a subcommittee.
Where the larger group has a name other than "committee" - for example, "Board" or "Commission", the smaller group(s) would usually be called committee(s), not subcommittee(s), and might go by an entirely different name, or substitute "Commission" for "Committee". For example in the sciences, the "International Commission on Stratigraphy" (ICS) a standing working committee is doing organizational work establishing uniform naming and benchmarks in the geologic record and timeline since 1974, all under the auspices of the International Union of Geological Sciences (IUGS). It is technically the "International Stratigraphy Committee" (ISC), which has limited executive committee powers to impanel other subcommittees (also called commissions) to resolve certain matters involving the Geologic time scale—its deliberations and those of its subcommittees must be adopted by the IUGS which meets in a committee-of-the-whole or Congress, every four years or so to deliberate on the subcommittee recommendations and officially adopt or not-adopt such.
From the foregoing, it can easily be seen subcommittees can generally be classified further by the adjectives: "Executive", "Standing", and "Working":
A subcommittee which has well defined executive powers usually spelled out in the charter or by-laws and which meets frequently to manage the affairs and further the purposes of an organization or entity. These are commonly empanelled as well when an organization has a large Board of Directors such as an international labor union, large corporations (with thousands of stock holders) or national and international organizations. A Board of directors is itself a kind of executive committee established by the charter and by-laws of the entity and elected by the overall franchised membership. For organizations where the Board of Directors is large - say 20 people or more - it is common to have an Executive Committee of the Board—an executive subcommittee of Board members, which is authorized to make some decisions on behalf of the entire Board.
A committee established by an official and providing for its scope and powers. Most governmental legislative subcommittees are standing committees, which by another name is a permanent committee. Standing committees meet on a regular or irregular basis dependent upon their enabling act, and retain any power or oversight claims originally given them until subsequent official actions of the committee of the whole (changes to law or by-laws) disbands the committee.
An ad hoc committee established to accomplish a particular task or to oversee an ongoing area in need of control or oversight. Many are research or co-ordination committees in type or purpose, and can be temporary. Some are a sub-group of a larger society with a particular area of interest which decides to meet and discuss matters pertaining to their interests. For example a group of astronomers might get together ad hoc to discuss how to get the larger society to address near earth objects; A subgroup of engineers and scientists of a large project's development team could meet ad hoc to solve some particular issue with offsetting considerations and trade-offs. The term when used officially, generally means a group with specific duties and related authority, so when encountered in official contexts subsumes all other official types of committees. The International Commission on Stratigraphy and its subcommittees (commissions in name) are working committees that meet both far more regularly and more frequently both in deliberation and co-ordination furthering the needs of the IUGS (which regularly schedules meetings only every fourth year) and the larger scientific community.
Committees are a necessary aspect of organizations of any significant size (say, more than 15 or 20 people). They keep the number of participants manageable.
Committees are a way to formally draw together people of relevant expertise from different parts of an organization who otherwise would not have a good way to share information and coordinate actions. They may have the advantage of widening viewpoints and sharing out responsibilities. They can also be empaneled with experts to recommend actions by the committee of the whole in matters that require specialized knowledge or technical judgment. A "Defense" or "Banking" subcommittee in legislative bodies or the many International science commissions such as the ICS mentioned above, or a local "board of health" are or may be such.
A conference committee is a joint committee of a bicamerallegislature, which is appointed by, and consists of, members of both chambers to resolve disagreements on a particular bill.
A standing committee is a subunit of a political or deliberative body established in a permanent fashion to aid the parent assembly in accomplishing its duties. A standing committee is usually granted jurisdiction over a particular area of legislation by the parent body.
A steering committee is a committee that provides guidance, direction and control to a project within an organization. The term is derived from the steering mechanism that changes the steering angle of a vehicle's wheels.
Project Steering Committees are frequently used for guiding and monitoring the information technology projects in large organizations, as part of project governance. The functions of the committee might include building a business case for the project, planning, providing assistance and guidance, monitoring the progress, controlling the project scope and resolving conflicts.