Standard terminology for function calling in languages that have named parameters (i.e., almost all of them). If you have a function f(int $a, string $b) and you call it with f(10,"gzarp!"), then it is said that the parameter $a is bound to the argument 10, and the parameter $b is bound to the argument "gzarp!". (Or vice versa -- "gzarp!" is bound to $b, but binding is reflexive so it doesn't matter all that much. Though you could have multiple arguments bound to the same parameter in a language like Perl6.)

Regex matching is really an operator, not a function call, but the terminology is the same. Well, except you'd probably call them operands instead of parameters.

Or at least, this is the way I think about it. The terminology always made sense to me because for a long time when I started writing perl, I just used /.../ and therefore left the match string bound to the default $_. (I didn't even know there was a $_ for a while; it just all somehow magically worked out when I did a while(<>) loop.) At some point, I had a string in my own $variable that I wanted to match, and "binding" seemed as good a word as any to describe how to set the string that I was applying the match to.