Railing

1. The action of a person watching a poker game as it happens, either live or online.

Explained

A player who is not in on the action will often be found railing those that are playing in a game. Usually a railbird is someone who is broke, but often times someone might be railing a relative, stakehorse or close friend.

In a Sentence

Sometimes the expression 'railing' is used online on a message forum. For example:

"You can chat with Bobby Joe, he's not playing but just railing OMGClayAiken."