Read someone's blog on history - the writer was curious as to the difference between concept and category (because she wanted to study gender as a concept and could only find it written about as a category). So I looked up
1. A general idea derived or inferred from specific instances or occurrences
1. A specifically defined division in a system of classification; a class.
2. A general class of ideas, terms, or things that mark divisions or coordinations within a conceptual scheme, especially:
Aristotle's modes of objective being, such as quality, quantity, or relation, that are inherent
So I decided that category is the better word to use because it speaks of ideas in terms of being parts of a bigger context. Since I don't believe hardly anything can be studied by itself, but always needs to be considered in terms of what it is bounded by, and since any study of a concept would be (or at least should be) interested in the boundaries of the idea in question, it seems that category is a more useful term.