the navy of the United States of America; maintains and trains and equips combat-ready naval forces

The common abbreviations for the U.S. Navy and U.S. Navy Reserve.

United States Navy

referring to the genus _Usnea_, a lichen ("usneoides," - the specific name of _Tillandsia usneoides_, the Spanish Moss)

Unique school number

update sequence number. In Active Directory replication, a 64-bit counter that is maintained by each Active Directory domain controller. At the start of each update transaction (originating or replicated) on a domain controller, the domain controller increments its current USN and associates this new value with the update request.

Update sequence number. A 64-bit unique number for tracking updates to AD properties. An integral component of the AD replication scheme.

United Space Nations. an advisory council, the USN is the successor of the 20th century's United Nations.