Jokes, especially nerd jokes, should never be explained as it just reveals how bad they were in the beginning.
Cobol is an ancient programming language that originates from 50's. It's designed by a governmental committee and the syntax is English-like and very wordy. Basically what you could do in some other languages in few lines would take Cobol several pages of writing; or at least that's how it felt.
However it was used by many big corporations like banks and insurance companies to build their whole systems. When the new languages run circles around Cobol the number of people who were proficient in it went down but the systems still needed maintaining. And being huge systems that were run 24/7 making changes and fixing errors were tough; thus everyone was happy to avoid any of that.