What is the name of the hypothetical middle-weight class of black holes between stellar and supermassive black holes?

The hypothetical middle-weight class between stellar and supermassive black holes is called intermediate-mass black holes.

Intermediate-mass black holes are generally discussed as objects with masses roughly between 100 and 100,000 times the mass of the Sun. They occupy the gap between stellar-mass black holes, made by the collapse of massive stars, and supermassive black holes, which inhabit many galactic centers.

Astronomers have identified several strong candidates, including objects in dense star clusters and ultraluminous X-ray sources, but the population remains harder to confirm than the other two broad classes. Their possible formation routes include repeated mergers of stellar-mass black holes or the collapse of very massive primordial stars. Finding them could clarify how the first supermassive black holes grew in the early universe.