Climbing Calls

Climbing calls have been developed for clear communication between the leader and the second during a climbing session.This should be called out loudly and clearly without adding any words to these calls to avoid confusion. When in a busy route, always use climbing partner's name.

ON BELAY	Climber says this to ensure that the belayer is ready and alert.
BELAY IS ON	In response belayer will reply to indicate that he is prepared to belay, after  making sure all knots, gates shut, tight on belay, in line with belay and able to brake correctly
CLIMBING	Climber will say this to let the belayer know he is about to begin the climb
CLIMB ON	Belayer's response indicating that he is ready and the climber can begin  climbing   *The above rock climbing calls are usually done in order on the ground prior to a climb after all necessary checks on the equipments have been conducted.*
TAKING IN	Belayer will take up any slack in the rope requested by the climber.
SLACK	This is requested by the climber so that the belayer will give some slack,  usually during clipping/unclipping of runner or top climbing.
TIGHT!	Often called by the climber, either when making an awkward move, or when expecting to fall off.
OFF BELAY	Climber says this when setting up a rappel at the top of a route so that the belayer knows that the climber is tied off to an anchor.
ROPE!	Call to warn other climbers when lowering or throwing out a rope or  abseiling, top roping etc.

These are the usual calls in rock climbing and must be agreed upon by the group before the climb.

source:
http://ezinearticles.com/?Different-Climbing-Calls---You-Better-Know-It-Well-Before-A-Climb&id=508976