What's the meaning of "()" in a function call?

Now, I usually call a function (that requires no arguments) with () like this:

myFunction(); //there's empty parens

Except in jQuery calls where I can get away with:

$('#foo').bind('click', myFunction); //no parens

Fine. But recently I saw this comment here on SO:

"Consider using setTimeout(monitor, 100); instead of setTimeout('monitor()', 100);. Eval is evil :)"

Yikes! Are we really eval()-ing a string here? I guess I don't really understand the significance and implications of 'calling' a function. What are the real rules about calling and referring to functions?