Here, it is used to refer to a batch file that is entered one or more times after it has been invoked, usually by jumps from other batch files that it invoked. Reentrancy differs from recursion in that the reentry does not automatically return to the calling batch file. Reentrancy is sometimes used from within the same batch file, as to restart with a specified environment size or to split an environment string into fields. Return the process by which code that has been called as a function or subprogram causes executation to resume with the instruction following the calling instruction when the called code terminates. Script a file containing a series of program instructions that are interpreted by an executable program.
Batch files are scripts.
The term is borrowed from card games - one or more designated cards can be used in place of any other card. Similarly, wild cards can be used in file names used as arguments to many commands to stand for one or more other characters, but cannot be used in real filenames themselves. It was not a great distance from using it as a recursion marker to using it as the name of a throw-away file. That lead to variations. In every case, the symbol is used because it is a good wager that there is nothing important in any directory that has the same name as my transisent file.