A Grom (plural Groms) is a word used repeatedly in the show. It is a title given to members of the cast (the main characters).
It is derived from an actual word grom, the shortened form of the term grommet (alternatively grummet). This in turn originated from the obsolete French gromette ("curb chain"), an alternate spelling of gourmette which came from "gourme" + -"ette".
The use of the term is apparent in many episode titles and events in the show: