Refers to the leftover mess when a man ejaculates (usually through masturbation) without washing his hands, leaving traces of semen on his hands or other parts of his body. Others near the carrier of the ghost load often come into contact with the body part afflicted by the ghost load without ever knowing it, hence the term "ghost" load.
Can be used as a noun or a verb, i.e. "ghost loaded".
John: "Sorry boss, I forgot to wash my hands after my mid-morning whack. I think I got ghost load on that Rep from Anderson Corp. when I shook his hand."
Jack: "It's mistakes like this we can't afford to make, John! You're fired!"