The literally definition is wishing somebody good night. It stands for good night man, then you follow to give the person a pound either in person, or through the internet/phone. Even when you are in person, you have to say I did, or did it. When you are on the phone, or internet, you have to physically touch the phone with your knuckles. One person says Knuckletouch/I did it, while the other says Knuckles/Did it.
After saying this, this is the end of the conversation with that person, and if you guys talk again, you have to end it with this saying.
"Alright man" (in a conversation, bringing it to the end).
"Gn man. Knuckletouch. Did it."
Gn man. Knuckles. I did it."