A phrase coined by Erica Jong in the book "Fear of Flying". As described by her - It is a sexual encounter between strangers that has the swift compression of a dream and is seemingly free of all remorse and guilt. It is absolutely pure, there is no power game and it is free of ulterior motives. It has also been described as the perfect one night stand.
The zipless fuck is the purest thing there is, rarer than the unicorn and I have never had one. - "Fear of Flying"