Adequacy: Beliefs are adequate if they are sufficiently like the truth for some purpose, and then their adequacy is relative to that purpose.
The reason to introduce this term in the given sense is that there is considerable need for it, since many beliefs and theories people have are adequate (or supposed to be) while not being "all of the truth and nothing but the truth". This includes most of science, most of faith, and most of one's beliefs about reality and other persons: Often, the best one can hope to get in the way of true beliefs about these subjects are adequate beliefs, to the best of one's knowledge, that depend on the evidence, and may need some or radical revisal when one knows more than one presently does.
It should be noted that what is adequate may depend much on one's purposes, and thus that what may be adequate for some, say laymen, may be not for others, such as professionals.
The central point about adequacy is the belief or fact that a certain belief when adopted will help one to reach a certain end, and that if this is so the reason is (often) that the belief is true in some respects. A good analogy is the sort of maps one needs to find one's way when trying to realize some end: Sometimes a mere sketch on the back of an envelope is all that is needed, other times one needs a lot of detail without which one cannot realize one's end.