Your climbing harness, which basically connects your body to your climbing rope, is a complicated piece of equipment. It has lots of parts-straps, buckles, and loops. Here's a breakdown of all the parts of a climbing harness so you know what you're looking at when you go out to buy a new harness.
The waist belt is the thick slab of webbing that wraps around your waist. It's usually sewn and padded for comfort, especially on big wall harnesses where you will be hanging in your harness for days at a time. Some harnesses, like those made for alpine climbing, have a no-frills waist belt with no padding but less weight.
The leg loops are the two wide, padded loops of webbing that encase your upper thighs. They can be adjusted by tightening or loosening the webbing which run through buckles. The leg loops are attached to the front of the waist belt at the belay loop and by adjustable webbing straps on the rear of the waist belt. The leg loop cross piece also attaches the leg loops to each other at the front of the harness. The leg loops work in conjunction with the waist belt to distribute your weight between your legs and pelvis in the event of a fall.
Harnesses have either one or two buckles attached to the front of the waist belt. A single buckle is usually threaded with a length of webbing on the waist belt and then doubled back on itself through the buckle. This ensures that the harness will not accidently come undone when it is weighted. It is extremely important to always double-check that your harness belt is doubled back through the buckle. Many harnesses also have double buckles that are prethreaded, which allow you to easily tighten or loosen the harness waist belt.
The tie-in loop is exactly that-a loop of strong, rigid webbing sewn onto the front of the waist belt. The length of webbing that secures the buckle is attached to the loop. When you tie your rope into your harness (using the figure-8 follow-through knot), the rope is threaded through the leg loop cross piece at the bottom and then up through the tie-in loop, which tightly secures the rope to both parts of the harness and distributes your weight on both parts if you fall or hang on the rope.
The belay loop is a strong, rigid loop of webbing that attaches the leg loops to the waist belt. The belay loop is also one of the most important parts of the climbing harness since a locking carabiner is attached to the loop when you are belaying or rappelling. The belay loop is extremely strong so it can withstand all the energetic forces of climbing, including severe falls. Still, belay loops have been known to fail, especially if they are old and worn, so always back it up to create redundancy in your chain of safety if you have any doubts about the loop's strength and integrity.
The gear loops, either soft or rigid loops attached to the waist belt, are used to rack your climbing gear, including nuts, cams, and quickdraws, to your harness for easy carrying while you climb. Harnesses usually come with either two or four gear loops, depending on the weight of the harness. Small harnesses for women or kids often have just two gear loops, while bigger harnesses have four. Usually it's better to have four gear loops, unless you're using your harness for gym climbing, top-roping, or sport routes. Most gear loops are not strong enough to support anything more than body weight.
A haul loop is a loop of webbing on the back of the waist belt. The best haul loops are sewn and are full strength. These are used for hauling a second rope on long climbs, aid climbing, and big walls. Some harnesses have a low strength haul loop, often a loop of plastic tacked onto the waist belt. These are usually used only for clipping a chalk bag or other gear onto the rear of the waist belt.
Leg Loop Cross Piece
The leg loop cross piece is a length of webbing connecting the two leg loops on the front of the harness. It is usually adjustable with a small threaded buckle. This webbing, along with the tie-in loop on the waist belt, is one of the points where you attach your climbing rope to your harness.