[OpenLayers-Users] Another Dumb Question?

[Bill Thoen]

In the example 
http://openlayers.org/dev/examples/custom-control-point.html, the line 
that says:

map = new OpenLayers.Map( $('map') );

I suppose this must return a reference to a div named 'map' but why wrap 
it in such a weird function? Wouldn't

map = new OpenLayers.Map( "map" );

work just as well?

I'm still pretty new to JavaScript and OpenLayers but I can't find a 
reference to the function $()  in my 5 lb JavaScript book (it's amazing 
what's NOT in the Rhino book!) nor can I find it in the OpenLayers docs. 
And Google seems to have a mental block against searching for anything 
that looks like punctuation even if I try "$()".

I'm especially curious because I also saw a reference to "library 
dependence on $" in the recent discussion about OpenLayers and jQuery, 
and don't know what it means.

So would somebody kindly clue me in on this one too?