A:
By definition (RONR p. 479), a committee "is a body of one or more persons, elected or appointed by (or by direction of) an assembly or society...."
The members of the committee are named when the committee is formed.
These are the only ones (plus any ex officio members, such as the President) who have the right to attend committee meetings, make motions, debate, and vote.
Put another way, non-committee members have no right to attend committee meetings; however, they may be invited to attend and express their opinions in a committee meeting formally called a hearing.
(See RONR p. 491.)