Words R Us - Biology
In biology, there are eight categories or classifications of all living things. The Domain describes all living things, then each category gets smaller as you step down the order.
For example, primates are a family, and humans are a species within that family, but we're not in the same genus as macaques: macaques have their own genus. Dogs and wolves are so closely related they’re in the same genus. The plural of genus is genera.
Generally these terms are based on latin and are common across languages, although a language may have their own name(s) for the term.
The NCBI Taxonomy statistics page displays the following information:
There are currently 73540 genera, 331418 species, and 23127 taxa of higher order. Since the number of taxa decreases with the genericity of the taxon, there are probably around 20000 families, give or take a few thousand.