Final answer:
Conference committees are ad hoc groups formed to reconcile different versions of a bill passed by the House and Senate, creating a unified piece of legislation for both chambers to approve before it becomes law.
Step-by-step explanation:
Conference committees play a critical role in the United States legislative process. They are established on an ad hoc basis when the House of Representatives and the Senate pass different versions of a bill. The primary purpose of a conference committee is to reconcile these differences and produce a single bill that both chambers of Congress can agree on. Members of the conference committee, drawn from both chambers, negotiate on the bill's contents. Once a consensus is reached, the revised bill is returned to both the House and Senate for a final vote. These committees ensure that legislation is thoroughly vetted and acceptable to both respective chambers before it can proceed to the President to be signed into law.
While conference committees are common for most major pieces of legislation, occasionally one chamber may decide to accept the other's version without convening a committee, as was the case with the Affordable Care Act. This step is sometimes skipped to expedite the legislative process. However, such instances are exceptions rather than the rule.