Final answer:
A main motion in Robert's Rules of Order is a formal proposal made to an assembly for discussion and voting, such as allocating funds for new library books.
Step-by-step explanation:
By Robert's Rules of Order, a main motion is a formal proposal put before the assembly for discussion and a vote. An example of a main motion, as recognized in Robert's Rules, could be: "I move that the club allocate $200 to purchase new books for the library." This proposal would then be open to debate, possible amendment, and ultimately a vote by the members of the assembly. The main motion is central to the decision-making process in formal meetings and is used to introduce new business or ensure a matter is considered and determined by the group.