Bit Character
A Bit Character is a minor character in the cast. She or he has a slightly larger part than the extra or the Spear Carrier, but isn't a well-known actor taking a small part, like a Cameo. The British television industry often refers to these as "under sixes" (six being the number of spoken lines required to no longer be a bit part). Similarly in the US they are "under fives".
While an extra is the guy walking down the hall carrying a stack of papers—basically a piece of animated furniture—the bit character is the receptionist who briefly interacts with the heroes, telling them that Mr Jones is too busy to see them right now, before turning to do other things.
The Bit Character may have a small role, but that part can move the plot along in some way (possibly for the worse), or let them serve as a Foil to a major character to flesh out the characterization. They could even be someone who gives the hero a piece of useful information, when the hero usual source has run dry or is unavailable for whatever reason. While they might have some eccentricity to make them interesting, a bit character is generally a Flat Character, to prevent the question of What Happened to the Mouse? from arising.
Some actors make a decent living playing bit characters throughout their careers, never moving up the hierarchy to "star". Such actors are called "bit players". Before she played the lead in the 1957 TV series The Adventures of Tugboat Annie, Minerva Urecal was a bit player in the movies.
Super-Trope of Bit Part Badguys, Very Punchable Man. When the apparent Bit Character returns with importance, it's Chekhov's Gunman.