The difference is in the defaults, not the product. There are two distinct cuts of pork used for bacon: belly and loin. In the US, belly is the default ‘bacon’,

The difference is in the defaults, not the product. There are two distinct cuts of pork used for bacon: belly and loin. In the US, belly is the default ‘bacon’, and to get bacon made from pork loin you need to look for ‘Canadian bacon’ (but that will have the fat all trimmed off) or ‘Irish bacon’, or you might find ‘back bacon’ in a butcher or deli counter. In the UK the default ‘bacon’ is back bacon, made from the loin. If you want belly meat you need to look for ‘streaky bacon’. Weirdly I think this is a case where US FDA regulations are oddly strict about what can be sold as ‘bacon’ and how it has to be packaged (those weird little fat windows in the cardboard) which prevents back bacon being offered as a normal product.