Many tech companies give employees restricted stock units (RSU's) as part of their compensation package. What that means is that you get a certain number of shares that you're restricted from selling until a certain point (that point is when the stock vests). It's usually on a a percentage of the stock vests after a year with the company, another percentage after another year, etc. The idea is basically that if you as an employee want to get rich selling stock that you need to commit to the company for a certain amount of time (and not just to stay but to actually work hard because you have an incentive for the stock to be high when you can finally sell it).

When tech company employees have stock that's vested (ie, they've sold part of it and are now wealthy), they are considered The Vested. You can say things like "life and times of the vested" or "the problems of the vested."

For an example of use of the term in the wild, see this Valleywag post....or this one.

See also: Twitter millionaires