Difference between Delegator and Delegation


I have an address, X, which is delegated to baker Y but says Delegatable: false in tzscan. I attempted to withdraw this delegation and that failed with error message Contract X is not delegatable.

On tzscan, X appears in the Delegators section, but not in the Delegations section. I have another address, Z, which does appear in both sections. Z says Delegatable: true and I successfully revoked the delegation from baker Y with address Z.

So, what is the difference here between delegation and delegator?