A shared abbreviation that can mean one of many things (the most common): No Strings Attached & National Security Agency.
No Strings Attached is a common English Adverb / expression that refers to no other obligations or responsibilities in a deal. The abrev. NSA has become connected to the casual sex terminology as someone wishing to engage in sexual activities while being free of all responsibilities associated with a romantic relationship.
Many people believe the National Security Agency operates much like the CIA, however, the NSA is a division of the US Defense Department and specializes on the protection of all US Government Communication & Information Systems. The NSA is limited to information surveillance (national and international only) and does not engage in human intelligence activities.
Other such abbreviations: National Shipping Authority, National Standards Association, National Student Association, National Scrabble Association, Niagara Soccer Association, National Scrabble Association, etc. etc.
"25/f/Vancouver NSA looking for a good time" - Craigslist