A fleet is a group of vehicles, often focused on a single discipline, that are owned and managed by a single company, non-profit organization, or government organization. The definition of a fleet is quite simple: any company or person that has more than one car has a fleet. Technically, the company doesn't even need to own the cars to be considered a fleet. Companies that use fleet vehicles often lease them to their employees instead of buying them.
Even employee-owned vehicles, if used for work tasks, can be considered part of a fleet.