usually it is an option or stock award grant that is valuable enough when fully vested over a long term (usually 4-5 years) that it is very hard to walk away from it. it "handcuffs" you to the company.
Golden handcuffs are a way to keep a key person at a company through massive payouts. For example the tumblr deal netted the CEO a massive golden handcuff of ~81 million to stay til 2017. [1]