The specific meaning of "recursive" in this context is "operating on a directory and its contents, including the contents of any subdirectories".
The word "recursive" is used here, because at least conceptually, this is easily implemented by a recursive algorithm:
procedure check_in_directory (d : directory)
for each entry e in d <== recursive exit after last entry in directory
if e is a file
if e is a directory
check_in_directory(e) <== recursive call
The recursive structure of this procedure matches the recursive definition of a directory:
This approach -- writing a function whose structure matches the definition of the data type you are processing is often referred to as structural recursion.