A cow is female whereas a bull is male. Depending on the species, either may have horns, but only cows will have udders.
Horns often differ in appearance between cows and bulls. For example, among Highland cattle, cows' horns tend to be longer and narrower with a finer tip than those of bulls.
Although people often refer to a herd of mixed-sex cattle as cows, this is just as technically inaccurate as it would be to call them bulls. The correct zoological terms for cattle, regardless of sex, are oxen or bovines, although the latter can also apply to buffaloes and bison.