Someone's stead is their position, or occupation. The eager understudy to starring role leapt at the chance to serve in the lead actor's stead when he mysteriously got food poisoning.
Stead comes from the Germanic root for "place, town," but we usually use it for a person's place, and most frequently when someone is serving as a substitute. If you serve in someone's stead, you're doing their job for them while they're not there. You probably intuitively know this word from the more common instead, which is just a shortening for "in the stead of."