Equidae: the scientific term for the horse family.  Equidae is a taxonomic family containing horses and related animals.  All the related animals are extinct, except those in the family Equus. 

The Equus family includes horses, zebras, donkeys, and onagers.  Not sure what an onager is?  Click here to find out.

Both equidae, and equus come from the Latin word for horse: equus.