How long an employee stays with a company is referred to as employee retention. Average or median tenure can also be used as a measure of how long employees remain with a company. The number of employees that leave a company in a given time, usually a year, is referred to as employee turnover. On the other hand, employee retention refers to how many employees a company manages to keep over a specific period. Tracking turnover is essential for businesses since it can be expensive to replace personnel. Retaining employees have a greater rate of return than recruiting new ones, like consumer retention.