Lardons can either be thin strips of pork fat used to "lard" meat (usually to add moisture to very lean cuts of meat that will cook for a long time - require the use use of larding needles) or it could be bacon that has been diced, blanched, and fried.
Like Andy M. noted - salt pork is salt cured and generally much fattier than bacon ... most bacon these days is smoke cured although you can find old-fashioned salt cured slab bacon from specialty suppliers.
What is your dish and how is the piggy-fat used?
"It ain't what you don't know that gets you in trouble. It's what you know for sure that just ain't so." - Mark Twain