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.
More About No Strings Attached
The benefits of a no-strings-attached relationship include uncommitted casual sex, the ability to pursue different options, and the opportunity to keep things light and casual. Because feelings often arise between sexual partners, it's important to be honest with partners when a no-strings-attached encounter is what you're seeking to ensure the other person feels the same and does not feel used, hurt or unimportant.