The phrase "protein supplement" suggests a substance that can be consumed to offset a protein deficiency. Searching the net for "protein deficiency", however, I was unable to find any sources describing the use of supplements for this purpose. In addition, searching for "protein supplement" yielded results consisting almost entirely of bodybuilding websites and fitness supplement stores.
Are protein supplements used outside of bodybuilding? If so, what are examples of their use?
Edit: I mean to ask about formal medical uses such as correcting recognized protein deficiencies.
Edit 2: I am not restricting this question to over the counter, commercially available products such as shakes and powders; I mean to ask about supplements in the general sense.