what is recursion when applied to the bash shell?

I keep hearing people talk about "recursion" for example, when you copy and paste a file and a directory you need to also put in the -r flag to tell the cp command to copy the directory "recursively" I look up the word "recursion" and I get this > recursion is when a function can call itself and then people tell me about russian dolls and how recursion is like a program inside a program like a russian doll is like a doll inside a doll. So my question is, what does "recursion" mean when it's applied to the bash shell? I don't understand how the concept of "recursion" applies to bash or the programs in bash for example when I cp a file and a directory and I have to put the -r flag in with cp to make sure that the file AND the directory gets copied