noun, tree sap or insect honeydew, secreted by insect colonies living in branches. Commonly found on cars parked under a large trees. The liquid is sticky and difficult to remove, residuals are white in colour and can damage paint work when dried. Removal becomes increasingly difficult as the tree semen dries up.
Shit man, that tree tried to inseminate my Bimmer last night, I got effing tree semen all over the bonnet, windscreen and doors.