You can assign backup approvers to your own assigned items, in order to allow these items to continue through the approval process without you. You may want to do this if you will be out of the office or just need help with approvals. 

Conversely, you may become a backup approver for someone else. This will allow you to approve items on another primary approver's behalf.    

Resources

• Managing Backup Approvers
• Managing Backup Approvers for Another User