Standard

When beginning work on a task, those in project management must have a set of expectations, guidelines, and rules by which their job is governed. This is called the standard which must be agreed upon by the agreement of members of a committee who have influence on the project. In many cases it is a group of those from project management who establish the standard for the job.
The standard must be established before any work begins. This ensures that the results are of an acceptable quality and done in an appropriate manner. By having a set of rules codified, workers on the project can accomplish their task in an orderly way without wasting time or resources. Project management must be sure to oversee employees to be sure that they adhere to the set of rules.
In many cases, the the standard is used for many different projects, with slight alterations for each job’s specific needs. Since those is management do not have to start afresh to draft a new set of guidelines for each project, their job is made more efficient. That is why the guidelines and rules in the standards are often repeatedly used for different projects.

This term is defined in the 3rd and the 4th edition of the PMBOK.