When I was at Google (2013->15), each we would receive equity in the form of GSUs which vested at 25% per year over four years. The idea was that each year you would get a new grant, and you would reach maximum income in year 4, when you had 4 grants vesting simultaneously.

In year 5, your initial grant would have expired, but your new grants would be vesting, so you would continue with 4 GSU grants vesting simultaneously, and you would stay at the same income (or better, or worse, depending on the size of your grants, the value of the stock, etc).

The idea is that your salary would be ~50% or less of your total compensation, once you factored in the GSU stock grants and the yearly bonus. It was so complex there was an internal HR site (go/totalcomp ?) that would try to break down your compensation.

The process is designed so that you reach "max" income in year 4 which does not substantially decrease, thus locking you in. Because if you left, it would take 4 years of tenure at the new company before you built up 4 simultaneously vesting grants.

All this is assuming you meet or exceed performance targets.

Frankly, I far prefer Netflix, where they just pay you every 2 weeks, and you're not waiting for grants to vest, or for yearly bonuses.