Counting the numbers: the concept of a quorum in the functioning of the Roman Republican Senate

Was a quorum of members present required to conduct meetings of the Senate or to approve certain types of decree? If so, how would such a requirement impact on the decisions made by the Senate? The word quorum does not appear to be a Latin noun. It does not appear in Lewis and Short nor in the Oxford Latin Dictionary. It is, of course, the genitive plural masculine of the relative pronoun qui, quae, quod, meaning in this case 'of whom' or 'whose'. In English it was first used to designate certain justices of the peace, usually of eminent learning or ability, whose presence was necessary to constitute a bench. Then it was applied to similarly distinguished members of other bodies and thus came to mean a select body. Finally, it came to mean 'a fixed number of any body, society, etc, whose presence is necessary for the proper or valid transaction of business'.