From How to Read a Book by Mortimer J. Adler:

You cannot find terms in dictionaries, though the materials for making them are there. Terms occur only in the process of communication. They occur when a writer tries to avoid ambiguity and a reader helps him by trying to follow his use of words. There are, of course, many degrees of success in this business. Coming to terms is the ideal limit toward which writer and reader should strive. Since this is one of the. primary achievements of the art of writing and reading, we can think of terms as an artistic use of words, a skilled use of words for the sake of communicating knowledge.

Let me restate the rule for you. As I phrased it originally, it was: spot the important words and figure out how the author is using them. Now I can make that a little more precise and elegant: find the important words and through them come to terms with the author. Note that the rule has two parts. The first step is to locate the words which make a difference. The second is to determine their meanings, as used, with precision.