1. To set off the tilt/motion detection device(s) in a pinball machine. Nudging the machine (within the limits of the detectors) in addition to using the flippers is a big part of the game (if you're any good), hence the sensitivity of the tilt sensors have quite a big impact on the game. Causing a tilt results (usually, but almost univerally) in the loss of the current ball and any bonus points built up during the current ball (these are otherwise awarded when the ball is lost). It has no effect on other players playing at the same time, and is hence considered perfectly socially acceptable. Causing a Slam Tilt (by hitting or attacking the door to the coin vault or other *very* violent behaivor towards the machine) immediatly ends the current game for you and anyone else currently playing and is hence considered very rude.
2. Gambling term (most common in poker) descibing an angry or "reeling" state of mind usually caused by a big or unluck loss. People playing on tilt play below their usual abillity and usually make larger and more aggressive bets to try to quickly recover their loss. In poker, this is very valueble to other players at the table, hence worth keeping track of and/or attempting to cause. People known to be prone to tilting are often taunted or generally aggrivated when they take a loss and then egged on when they do tilt in order to keep them in this state as long as possible.
This damn machine keeps tilting as soon as I touch it!
My stack was up to $250 but I lost $100 with a AA to a KQ and went on tilt. Before I knew it, it was all gone.