In LSAT terms what is an assumption?

Answer 1

An assumption is an unstated premise. I.e., a fact or statement that needs to be true in order for an argument to work, and yet is not directly stated in the text of the argument. For example, imagine the following argument.

All men are cool.

Therefore, Tommy is cool.

This argument works if Tommy is a man. However, the argument did not tell us that Tommy is a man. Therefore, "Tommy is a man" is an assumption in this argument.