The term opener for this crossword puzzle is MID, which is a three-letter word. MID is an abbreviation of the word 'MIDDLE' and is used to refer to the MIDDLE of something, such as the MIDDLE of a range or the MIDDLE of a sequence. It can also be used to refer to the MIDDLE of a period of time, such as the MIDDLE of a month or the MIDDLE of a year. MID is also used to refer to the MIDDLE of a group of people or things, such as the MIDDLE of a line or the MIDDLE of a crowd.