A helpful piece of information or advice that may be generally unknown or secret. Originated in GamePro video game magazine.
"Oh, you have Professor McGee? Pro Tip: don't say anything bad about gay marriage in her class; she's a lesbian."
An advice you didn't need, coming from a person who thinks he is better than you.
This can often be related to video games.
In a game of Dota/HoN/LoL
Mortane: dude your K/D is terrible, if you keep dying get some more HP
honrockzers87: ... I would if I could save up some gold...
Walroz: lol Mortane, pro tip!