Market capitalization ("market cap") is simply circulating supply times price. It's the standard way to compare the size of two assets that have wildly different unit prices and supply counts, a coin trading at $0.01 with a huge supply can have a far larger market cap, and represent a far larger, more established asset, than a coin trading at $100 with a tiny supply.
Market cap is a size ranking, not a quality or safety signal on its own. A large market cap generally correlates with deeper liquidity and more participants, but plenty of large-cap assets have still gone through severe drawdowns, and a shrinking market cap can persist for a long time before a coin is meaningfully "small" by any other measure.
zengtrade's coin universe is ranked by market cap specifically because it's a stable, hard-to-game ordering. Raw 24-hour volume, by contrast, can spike a low-quality, low-liquidity coin to the top of a volume ranking for a single noisy day.
Educational content, not investment advice. zengtrade is paper-first and non-custodial.