A more thorough explanation:

A master agreement is a type of labor law agreement that is made between a union and industry leaders. The terms of this agreement serve as a model for agreements that will be made between the union and individual companies within the industry.

For example, let's say that a union representing workers in the automotive industry negotiates a master agreement with industry leaders. This agreement will outline the basic terms and conditions of employment for workers in the industry, such as wages, benefits, and working conditions. Once this master agreement is in place, individual companies within the automotive industry will negotiate their own agreements with the union, using the terms of the master agreement as a starting point.

The purpose of a master agreement is to streamline the negotiation process between unions and companies within an industry. By establishing a set of basic terms and conditions that are acceptable to both sides, the negotiation process can be made more efficient and less contentious.