No strings attached (NSA) is a phrase used to describe a relationship that is exclusively sexual in nature. As an acronym, NSA is often used on dating sites when people are looking for a sexual relationship without any commitments or even emotional connection. Usually, people in an NSA relationship try to limit their interactions to just sex.
The origins of this term are unknown, but it was first added to Urban Dictionary in a sexual context in 2018. The more common definition of no strings attached - the offer of something without any special conditions - has long been used in a non-sexual context.