I'm assuming you are asking for the definition of the word "lat". "Lat" can have several different meanings depending on the context. Here are a few possible definitions:
A type of exercise: "Lat" is short for "latissimus dorsi", which is a large muscle in the back. "Lat exercises" typically refer to exercises that target this muscle, such as pull-ups, lat pulldowns, and rows.
A unit of measurement: "Lat" can be short for "latitude", which is a unit of measurement used to specify a location's position north or south of the equator.
An abbreviation: "Lat" can be used as an abbreviation for other words, such as "lateral", "Latin", or "latitude".
Without more context, it's difficult to determine the intended meaning of the word "lat".