One of the most important techniques in
climbing. Very simply, it is the act managing a rope, and being ready to `lock' the rope in case of a
fall. It is very important because often you are responsible for catching the fall of the person who you have on belay. This often means the difference between
life and
death.
A belay begins by having the leader tie the sharp end of the rope into his harness. The prefered knot for most climbers is the figure eight knot which is a modified form of the bowline. It is important to know that this knot should be tied directly into the harness, not through a carabiner, locking or not.
After the leader has tied in the person who is belaying will attach himself to a bombproof protection point. This will keep him from being pulled up the route in case of a fall by the leader. After the belayer is attached he will run the same rope the leader has tied himself into through a belay device attached to a locking carabiner on his harness. There are many types of belay devices, some of which are the figure eight, the ATC (or Air Traffic Controler), or even a Italian munter hitch. The ATC is generally the prefered belay device.
A belay device is basically a way of applying friction to the rope. Without friction the rope will be able to slide somewhat freely both ways through the belay device with help. When the leader falls, wishes to hang, or has a need to pendulum, the belay will increase the coefficent of friction by pulling the rope against the side of the belay device while gripping the rope tighter.
Once the belay is setup the leader will request "On Belay", and the belayer will reply, "Belay On." This indicates that the belayer is aware and watching the leader and fully ready to catch him, or lock the ropes slide if he sees or hears him falling.
The leader will now climb the route, placing protection in the rock or ice face. Protection comes in the forms of bolts, cams, pitons, nuts, hexes, ice screws, or slings. Each piece of protection will have a quickdraw attached to it. There have been many discussions on the placement of the gates of the quickdraw, however, it's generally known that the bottom carabiner's gate shold face opposite the direction of travel. This helps to prevent the rope from looping on itself and unclipping from the carabiner.
Of course, protection is not always bombproof. In the case of some falls the belayer has caught the leader and the leader has fallen down the route ripping protection off the route, only to be caught by the last protection.
It is however, quite common to fall. This is why an aware belayer is vitally important. Never climb while being belayed by a person you don't trust.
There are some mechanical belaying devices which help the belayer. The best of which, I believe, is the Petzl GriGri. It works like a seat belt, allowing rope to slide in both directions, but as soon as there is a violent outspelling of rope it will lock. This might not work always though, and constant awarness is always required on the part of the belayer. Sometimes the friction of the rope running through the quickdraws won't be enough to excite the GriGri into action. This is why the leader will often shout "Falling!" to make the belayer aware that he should lock the rope.
Part of rock climbing is falling. You will fall tens, hundreds, and thousands of times depending on how you climb and how aggressive you are. Most of the time the fall is caught, and you can swing back to the rock, and continue climbing.
Falls on ice, however, are a little more scary. Ice screws can absorb a fall, only to have the energy from that fall melt the ice around the screw away and cause the leader to fall more.
Some terms that come with belaying are belay slave, and belay monkey. Both of which mean that that person is being patient while crinking their neck belaying you all day long. This might be a girl who you're impressing, or just your friend who woke you up at 6:30am and pleaded with you to drive him to Chem Lab because his car was broken and it was cold outside.