The zipper is a two handed sex move performed on a penis by someone else. Basically, while kneeling in front of your partner, you interlace your fingers grabbing the penis with both hands and rhythmically stroking it in a back and forth manner. This hand position is superior due to the added friction and position of the hands to apply more pressure with least amount of effort.
James said, "Wow that girl was skilled in bed last night, she performed The Zipper on me, Amazing".
Rob replies, "Damn your so lucky, I wish my girl knew about The Zipper".
Kevin exclaims, "Whoa, I gotta run back to the "love nest" and teach my girl The Zipper right now".