Gammon is the traditional name in United Kingdom. Outside that tradition, butchers carry comparable pork cuts under different names — sometimes the same anatomical piece, sometimes a close cousin. The alternatives below are grouped by country so you can match what your local butcher actually carries.
Both cured European pork legs, but Black Forest ham is cold-smoked over fir and eaten raw, while gammon is wet-cured (sometimes lightly smoked) and eaten cooked.
Both cured pork legs; Westfälischer is cold-smoked over juniper/beech, gammon is wet-cured for cooked consumption.