Adjunct professor
From Conservapedia
An adjunct professor refers to a part-time non-salaried, non-tenure track faculty member who is paid for each class they teach. It is not considered a permanent position, and is usually part-time with no benefits. Often, it is someone with outside expertise in a specialized area.
Adjunct professors are generally cheaper to hire, resulting in a reduction in the number of tenure-track faculty at many universities and colleges.[1]