Fruction is a "farting" sound that happens while fucking due to the skin-to-skin friction.
Fruction normally happens when two people are having sex. When having sex, your body tends to sweat. The sweat then settles in you secretions. With all this sweat and skin to skin contact, this can cause a "farting" sound.
Fruction is made from two words;
Fucking & Friction
When these two words are put together, you receive the term Fruction.
We were going at it last night and suddenly I fructioned and I had to go wipe myself off.