In online poker, to observe tables with the intention of collecting information on how other players play in the form of hand histories.
At one time it was argued that this is data collection rather than 'mining' per se but the term appears to have become accepted terminology in online poker circles.
Am I a huge online poker underdog without data mining? (Two Plus Two forums)
A sunburn or suntan focused on the left arm. It is caused by the left side of the body being the only half that gets exposed to sunlight while driving. Presumably, it would be located on the right side of the body in countries where they drive on the left side of the road.