The word "mid" is an abbreviation for "middle." It can be used as a noun, adjective or adverb to describe something that is in the middle or between two other things. For example, you could say "the midpoint of the bridge," meaning the center of the bridge, or "a mid-sized car" meaning a vehicle that falls somewhere between small and large in size. As an adverb, it can be used to describe something that is moderate or average, such as saying "he spoke midway through the meeting."