Market cap
Also called: market capitalization
The current price multiplied by the number of units in circulation.
In practice
On a quote page it tells you the scale of the asset — a $1.2T market cap moves differently from a $6B one, because it takes far more money to move it.
What it is not
Not price times every coin that will ever exist — that larger number is the fully diluted valuation, and in crypto the gap between the two can be big. Also not money anyone actually paid: nobody bought the whole supply at today's price.