Like prosciutto and other hams, speck is made from the hind leg of the pig, but, unlike other prosciutti, speck is deboned before curing.
Bacon is prepared from several different cuts of meat. It is usually made from side and back cuts of pork, except in the United States, where it is almost always prepared from pork belly (typically referred to as "streaky", "fatty", or "American style" outside of the US and Canada). The side cut has more meat and less fat than the belly. Bacon may be prepared from either of two distinct back cuts: fatback, which is almost pure fat, and pork loin, which is very lean.
tl/dr: speck is smoked ham, and is made using the pig's legs.
Bacon is made using back cuts or pork belly, and is not necessarily smoked.
Ahh thanks Vegio. That makes sense!