Self-basting is an expression used to describe a piece of meat that has been prepared or cooked in such a way as to baste itself. Normally the meat is fowl, particularly turkey, which is renowned for being dry.
The self-basting turkeys at stores are injected with mixtures of broth, fats, salt and chemicals, depending on the brand. If you want to see what was used, check the label. The solution injected will constitute 6 to 9 % of the weight that you are paying for.
Pork that has been plumped up with injected saline is also now sold; the processors defend the injections by saying that it makes the pork “self-basting”, and compensates for consumers’ tendencies to overcook pork.
See also the entry on Oven Bags, which are sometimes referred to as Self-Basting Roasting Bags.