What is the meaning of '' mark to market''?

mark to market means capturing the latest price of a stock that might be different in its purchasing price which represents its book value. example lets say you buy 100 stocks of ABC corp at $20 a share on Oct 15 and today oct 22 the stock closed at $25 a share for ABC Corp - this usually represents your mark to market value of your stock - this expresses either as a profit or loss i hope this helps