A techie climbing term you may come across is an “HMS” carabiner. What ‘da heck does this mean?
If you don’t speak German, it’s a reasonable question. It’s actually an acronym for “Halbmastwurf sicherung”, which in German means “half clove hitch”, another name for a Munter hitch. An HMS biner is thus a large locking pear-shaped biner, suitable for belaying with a Munter hitch.
(Side note - belaying the second with a Munter hitch directly off the anchor might seem a little old-school, but it is a very useful technique that every climber should know. Read more about how to do it here.)
In American climber slang, this sometimes gets shortened to a “pearabiner”, which is certainly more descriptive.
Look, they’re almost cousins!
One of the advantages of using a pear-shaped carabiner like this is that the bottom edge is wide and relatively flat. This offers a few benefits.
One, as the name implies, you can easily belay off of this with a Munter hitch, because the wide gap in the bottom allows the knot to flip back and forth as you take in or let out rope.
Two, the wide and flat bottom allows you to clip other carabiners onto it, and add them and remove them fairly easily, even if one biner is loaded. If you were to use a “D” shaped carabiner on your master point, the loaded carabiner will often pinch down on the other ones, making removal much more difficult.
This can be especially helpful on big wall climbing, when the first step to build an anchor is usually clipping a large pearabiner into each of the bolts, and locking the gates. Everything else you add to the anchor typically gets clipped into those primary carabiners.
(And, there are some old school safety police out there reading this, who are probably having a freak-out right now that I’m advocating clipping one carabiner on to another. Don't worry, they’re lockers, and it's fine to do it at an anchor. But if you don't like it, you don't have to.)
Close up of master point with an HMS / pearabiner, showing 2 biners clipped to it under load.
This German origin of the term HMS is from “The Mountaineering Handbook” by Craig Connally