Models are eXtensive Markup Language files saved as *.RBXM. ROBLOX parses them, and reads the info of all of the objects as stored, from their shape, position, and color, right down to their relative locations.
Main use
Models are used to either save an object so that the data of the models aren't lost or to allow other users to use them in Free Models.
Models are also sometimes used to create new or retextured hats. Users can create and showcase a model of a hat in some posts on the forum and could use the hat model in order to be sent and wait for the hat model to be published as an actual hat by a moderator.
Some Models are very simple, such as two CFramed bricks, and some are very complex with numerous amount of scripts.
How to upload an ModelAn example of a model. This is Legokid, a well-known model.