Desu is a common word to hear at the end of a Japanese sentence, and it functions similarly to words such as "is" and "to be", except the Japanese put it at the end of a sentence instead of the middle because they like to make things hard for English speakers. The sentences "this is a computer" and "let's go to the shop" for instance would end with -desu when translated into Japanese, I think. My Japanese is really bad, but I believe this is how it works.
When watching anime in Japanese, you would hear -desu a lot at the end of sentences, so it would be something that sticks out to a lot of viewers who don't speak Japanese. This probably had something to do with the term initially gaining popularity.