OK, Here's what I've worked out over the last 12 months of study, mainly from this forum, but also through other media and enthusiast sites...
The term "ham" can mean a raw cut of pork leg, and it can also mean "any" part of the delicious pig that has recieved a wet cure and has been turned into "ham" via brining and smoking, either cold smoke or hot smoke.
As a result, there is picnic ham, or shoulder ham, taken from the shoulder of the pig, as well as lot of other varieties of ham, the world over that are made from the loin or the neck (butt) etc.
Bacon in the USA is typically only made from the belly in commerical form.. like Hormel and Oscar Mayer Bacon etc... (Which I used to buy in Hong Kong when I lived there). Buckboard bacon is made from the pork neck (or butt) with a dry cure.
"Bacon" comes in a wide variety of interpretations in other places in the world. I've made bacon like this:
We call this "middle" bacon and we call belly bacon "streaky" bacon.
English and Europeans have a multitude of other interpretations made from various cuts where the distinction between whether it is a ham or a bacon can be pretty blurry: Take your classic italian prosciutto. It's salt packed and air dried for months... stronger than a bacon by many orders of magnitude, yet is still considered a "ham"... because it comes from the leg... the ham cut.
Canadian bacon goes the other way. It's more like a ham because it's brined, not dry cured. The pork loin is the cut from the "back" or top of the pig (where the term "eating high on the hog" comes from. Canadians call it "back bacon", and because Canadians do it, Americans call it "Canadian Bacon".. its proper terminology is more like a "loin ham".... and in Europe there are a lot of commercial hams made just this way...
Clear as mud??? Oh... yeah, I better add... I could be wrong though...