I've seen the term fall out of usage. Years ago, when Bitcoin made up 90% of the cryptocurrency market cap, and nearly every other cryptocurrency was a fork of Bitcoin, with a name that was some variation of *coin (e.g. Litecoin, Peercoin, Dogecoin, Novacoin, BBQcoin) it made sense. Not so much now anymore, with Bitcoin's market cap under 50%, and original projects being its major competitors.

Market cap is a poor way to measure each coin. You can create your own coin premine 1 million of them. Sell a few for ~5 dollars and claim it has a market cap of 5 million dollars.

Market cap can be a totally valid way to measure total worth. In the case of a cryptocurrency with a large circulating and trading volume, like Ether, it's a reliable measure of total value.