I'd have to disagree slightly with Dave's link that tries to explain the difference between bacon and ham.

Bacon is a term for pig meat that is dry cured and (sometimes) smoked. Virtually any part of a pig can be turned into bacon.

Hams are the hind legs (thighs) of pigs. They may be prepared as bacon, or in any other number of ways.

'Ham' is part of the pigs anatomy, 'Bacon' is a preservation method.