Jaap Arriens/NurPhoto via Getty Images
"Market cap" — short for "market capitalization" — is the total value of a public company's outstanding shares, which are those owned by stockholders, not by the company itself. Outstanding shares can be owned by employees and board members — just not the actual corporation.
A way to think about a market cap is that it's a company's value in good faith; after all, shares are an intangible asset, not a physical item, so they are worth nothing if no one wants them.
Through that lens, Apple is doing very well based on its market cap, which ranks it among the world's most valuable companies. And it looks like the company's best days may well be ahead.