"Netflix and chill" is a slang term that became popular sometime in 2015 for sex. Much like the earlier "Come up and see my etchings", the euphemism comes for inviting someone over for a seemingly innocent, even bland activity, which is a pretext for a romantic or sexual interlude. The origins and popularization of the term remain unknown, it seems to have risen spontaneously out of the hivemind of the internet.
The term brings up two interesting issues for me. The first is how quickly television, once considered one of the most passive and unsocial forms of entertainment, has become an exciting enough activity, that it can be the cover activity for sexual meetings. The second interesting issue is that in a time fifty years after the "sexual revolution", when premarital sex is considered normal and accepted in most social groups, and when there is much less shame involved with casual sexual activity, there is still a need for euphemisms and pretexts to have sexual activity, or at least there is still room to make jests and innuendos about such things.