Delegated Approver is an alternate approver.

This user receives the same approval requests as you do.

Delegated approvers can’t reassign approval requests. But, they can approve or reject approval requests.

Having the “Record Editability” setting set to “Administrator OR Current Approver” does not apply to the delegated approver.

https://success.salesforce.com/ideaview?id=08730000000BrJYAA0