I have never head that term before, but it sounds like it means a macro that refers to itself, otherwise known as a recursive macro. An example in m4 would be the factorial function:
define(`factorial', `_$0($1, 1)')dnl
define(`_factorial', `ifelse($1, `0', $2, `$0(decr($1), eval($1 `*' $2))')')dnl
Basically, if you give factorial the argument of 0, it returns its internal counter, which defaults to 1. Otherwise it multiplies a counter by your argument, decrements the argument, and calls itself again.