The word “tertiary” is an adjective that means “of third importance or rank”. It is often used to describe something that is less important than two other things. For example, you might say that your “tertiary” goal is to learn how to play the guitar. This means that learning the guitar is less important to you than two other goals, such as finishing school and getting a job.
The word “tertiary” can also be used to describe something that is third in a series. For example, you might say that the “tertiary” stage of a project is the testing phase. This means that the testing phase is the third stage of the project, after the planning and development stages.
