Serving status explained
Serving status displays information on whether an account, budget, campaign, ad group, ad, or keyword is actively serving.
Note: Serving Status is not the same as Status. The Status column simply shows whether a specific element is paused, enabled, or removed.
It's possible to have an enabled element that is not serving. For example, an account placed on a Manual Hold will contain campaigns that aren't actively serving, yet may be enabled.
Possible statuses
Eligible
Budget Hold
Manual Hold
$0 Budget
Read Only
Over-Pacing
Pending
Ended
Paused
Removed
Missing
Inactive
Serving Problem
Learning
Blocked