A key skill all rock climbers need to have in their repertoire is a solid understanding of climbing commands (calls and terminology). These commands are a standard form of communication that ensure the safety of the climber. They should be spoken clearly and loudly (sometimes shouted), and they should be used as is rather than couched in a sentence. When you are a long distance away from your climbing partner, it's more difficult to hear, so simplifying what you say is important. On the other hand, it is a good idea to use your partner's name.
Commands Said Before a Climber Begins
The first four commands a climber must know are: on belay, belay on, climbing, climb on. These commands are to be stated loudly before a pair of climbers begin climbing. The climber is the person climbing, and the "belayer" is the person who is securing the safety of the climber as she climbs.
First, the climber says "on belay" to notify the belayer that she has tied the rope into her harness and is ready to climb. Second, the belayer says "belay on" to let the climber know he is ready to belay her as she climbs. Third, the climber says "climbing" to let the belayer know she is about to climb. Fourth, the belayer says "climb on" to acknowledge the climber and let her know she can go.
While climbing, climbers say a variety of things including: "up rope"--when there is slack in the rope that they wish to have taken up; "slack"--when they want the rope loosened; "take" or "falling"--when they want their belayer to take the rope up tightly while they rest, and/or fall when they want the rope to support them; "watch me"--when they desire the belayer to pay closer attention.
Commands Stated at the End of a Climb
Commands said at the end of a climb include "off belay," which indicates the climber has made it to the anchor and is secured into that anchor and/or is securely on the ground. The belayer then says "belay off" to let the climber know she is off belay. If the climber is at an anchor, she may want to be lowered down to the ground, in which case she will say "ready to lower" or "got me?" in order to warn the belayer. The belayer will then say "I've got you." If two climbers happen to be at the top of a climb at the anchor and they are going to rappel down, the first climber to the ground will shout up "off rappel" to let the second climber know she has reached the ground and the second climber can now rappel.
Other Commands and Terminology
If a climber knocks a rock off the wall or drops a piece of equipment, he should always shout "rock" to let people below know that something is falling. He should do the same whenever he throws his rope from above by shouting "rope."
When the climber is leading a climb and clipping the rope into protection, sometimes he will say "clipping" to let the belayer know that he needs a bit of extra slack in order to clip the rope into the gear. Other times a belayer will take in all the slack in a rope to belay a second climber up to an anchor. When he pulls all the rope up, the second climber should say "that's me" to let the first climber know the rope is tight to the second climber.