Mid- is a prefix (a word part you attach to the beginning of other words) meaning “middle” or “in the middle of.” When you add mid- to a word, you're specifying that something happens in the middle of a time period, place, or process.

You see it in time words constantly: midday means the middle of the day (around noon), midnight is the middle of the night, mid-morning falls between early morning and noon, and mid-September refers to dates around the 15th of the month. If someone says they'll finish a project by mid-March, they mean sometime around the middle of that month.

The prefix works with places too: midair describes something happening in the middle of the air (like a basketball frozen in midair during a jump shot), midfield is the center area of a sports field, and the Midwest is the central region of the United States.

You can even use it for processes or actions: mid-sentence means in the middle of speaking a sentence, and mid-stride describes being partway through a step while walking or running.

Notice that mid- usually attaches directly to the next word with a hyphen (mid-afternoon) or runs together as one word (midnight, midway). The key idea never changes: something happening, existing, or located in the middle of something else.