Sweat Equity

Stock options. Employee stock options, that is. Maybe RSUs, or compensatory shares themselves as payment for your working at whatever.com in the early years, when the company had no cash to pay you.

You sweated as you worked, not in return for cash salary...but rather for a sliver of actual ownership in the company. If the company gets big and highly valued, you'll have made bank; if it goes bust, you worked for nothing other than the good vibes of failing along with the founders, owners, and investors of the company (i.e. next time get paid in cash).