Create a delegate for a Safe address

Question

In the docs there is a api call to add a delegate for a safe: https://safe-transaction-mainnet.safe.global/

Where the data object (body) is something like this:

Delegate {
  safe string
  delegate* string
  delegator*    string
  signature*    string
  label*    string
}

What is the delegate parameter referring to? Is a wallet address or is a delegate key, created via their app on IOS