Fleet tracking is a Management Solution that uses GPS to monitor the activity of tracked assets (vehicles, equipment, workers).  It is often referred to as vehicle tracking, AVL (Automatic Vehicle Locator) LBS (Location Based Services).  A fleet is generally a collection of assets such as cars, trucks, heavy equipment, field workers as well as powered and non-powered units such as trailers, light towers, Frac Tanks, etc.
The process of tracking uses telematics technology to collect data from a fleet of assets.  This data is normally collected in near real time (actively) so it is more useful for fleet managers, who use the data to make strategic decisions about operations (which vehicle should I dispatch to a new job, where is the nearest crane, how many generators do we have in the yard, has my lone worker returned from the jobsite etc).