Coinage refers to metal money, or coins. A numismatist — that's the technical term for a coin collector — is interested in coinage. Coinage is also the process of coming up with a new word.
You probably wouldn't refer to the dimes jingling in your pocket as coinage, since this term tends to be used for coins in a more collective way, as in the coinage of foreign countries. Another way to use coinage is for the process of inventing (or coining) a new word. Shakespeare is famous for a lot of literary achievements, including his coinage of words like "lackluster," "bandit," and "bedazzled."