OK... this one makes more sense than offside we have rules for similar reasons in Aussie Rules (Time Wasting & Deliberate Out Off Bounds) so its a rule to ensure continuous play .... I think I might even have it worked out...
So icing is when a player on team #1 shoots the puck across 2 redlines (ie the centre red line and Team #2s goal line) untouched and the puck is first touched again by team #2. The penalty is a face off (face off is the same as field hockey so no new knowledge required) in team #2s offensive side.
Exemptions:
a. If it happens when the team is short handed during a PP (yes I know PP is power play and I know hockey PPs are different to Cricket 20/20 PPs)
b. If the puck is collected by either Team1's goalie or another player from Team 1 touches it first, then the icing rule doesn't apply.