Salt Pork is brined pork belly, the same as bacon but not smoked, and with the skin on. It was formerly a very popular ingredient in American cuisine, but fell out of favor due to the American Heart Association's misguided vendetta against the natural fats we evolved with in favor of deadly trans fats. Back in the mid 19th century Americans practically lived on pig fat, and congestive heart disease was almost unknown then. This was actually pointed out by an elderly cardiologist at the kick-off for the AHA's "Heart Healthy Diet".
Now that much of the AHA's "modern medical knowledge" has been totallhy discredited, and even the role of saturated fats is being strongly re-examined, cooks can feel free to return to this flavorful traditional ingredient. Pig fat, by the way, has a better health profile than butter, even by the AHA's reconning - much less saturated fat than butter (44% vs 65%) and more of the healthy monounsaturated fats (45% vs 30%).
More on Cuts of Pork and
Pork Products.
Today, most Americans are familiar with this product only in the form of the one tiny piece included in a can of "pork and beans".