What is a group of rhinos called?

There isn't a specific, formally named group of rhinos like there is for some other animals (e.g., a pride of lions, a crash of rhinos). While you might hear people informally refer to a group of rhinos in various ways depending on the context (a "crash" is sometimes used, though it's not universally accepted for rhinos), there's no official collective noun. The best way to refer to a group of rhinos is simply "a group of rhinos" or "a herd of rhinos," acknowledging that they may or may not exhibit strong social bonds depending on the species and age/sex of the individuals.