It's the sweat that accumilates under big boobs

The act of ejaculating on the image of Queen Elizabeth's face on a British bank note, then using the ejaculatory fluid as a natural adhesive to stick the bank note to your partner's face.

This was traditionally done with a five pound note, but due to the 2017 release of the plastic five pound note, (which is less absorbent) has changed to the ten pound note.