What most people refer to as an employment contract is a written document between the employer and the employee. The most common is the union contract that the union obtains for its members.
An employment contract is a document that includes the details such as the type of work, how the work will be judged or delivered, the pay, what happens if either side is not satisfied, and most importantly, how long the contract will last. Many people who work as independent contractors or consultants use employment contracts.
That way they are assured of certain details about the work and the amount they will be paid.