“According to DoD,”:http://www.defense.gov/npr/docs/10-05-03_Fact_Sheet_US_Nuclear_Transparency__FINAL_w_Date.pdf that’s the number of warheads in the US nuclear weapons stockpile.

The stockpile, the “fact sheet”:http://www.defense.gov/npr/docs/10-05-03_Fact_Sheet_US_Nuclear_Transparency__FINAL_w_Date.pdf says, includes

bq. both active and inactive warheads. *Active warheads* include strategic and nonstrategic weapons maintained in an operational, ready-for-use configuration, warheads that must be ready for
possible deployment within a short timeframe, and logistics spares. They have tritium bottles and other Limited Life Components installed. *Inactive warheads are maintained at a depot in a non-operational status,* and have their tritium bottles removed.