A trademark application that has been declared abandoned is “dead” and no longer pending. Abandonment occurs under several circumstances. The most common reason is when the USPTO does not receive a response to an Office Action letter from an applicant within 6 months from the date the Office action letter was mailed.
Another instance is when the USPTO does not receive a Statement of Use (or request for an extension of time to file a statement of use) from an applicant within 6 months from the issuance of a Notice of Allowance).
Applications abandoned for failure to respond to an Office Action or a Notice of Allowance can be revived or reinstated in certain circumstances.