Controlled
descent of a rope usually with the use of a
carabiner or
descender.
Rappel. Its etymology is German for "down rope".
When I was in the army we always rappelled. That was in the mid 1980's. Lately, I see all the military correspondents using the term "abseiling." I'd never heard of it - had to look it up. I'm not sure why "rappel" has fallen out of fashion.