A Münter is a hitch that is tied onto a carabiner. You can use the Münter as a descent control "device" (aka a "DCD") when lowering a load or rappelling, or you can use it as a belay device which allows you to take in slack while being ready to catch a sudden load.
An advantage of a Münter hitch is you don't need any additional hardware. A disadvantage is it twists the rope. The twisting usually isn't significant if you rappel once or twice, but if you use the Münter repeatedly the twisted rope can become a real pain.
There are several different ways to tie a Münter. In this first method, you fold the rope on itself and then clip the two strands with a carabiner.
In this second method, you run the rope through the carabiner, create a loop, and clip the loop.
The Münter has the unique ability to change between a descent control device and a belay device. When it switches between these modes, the hitch changes its position on the carabiner.
The "critical point test" (aka "scissors test") requires that if any one item fails, nobody should be injured.
A "bend" is a knot that joins two ropes.
A "hitch" is a type of knot that must be tied around another object.
The "whistle test" requires that if all rescuers let go, nobody should be injured.