JavaScript, jQuery, and function(event)?

1

I’ve been working with javascript for years now, and I have something to confess. When did function declarations change? Did I miss something?

I know theres the typical function:

function blah(some_data){
  alert("this data is: " + some_data);
}

But I see things like this now:

blah.var = function(event){
//random stuff here
}

Also, jQuery has some interesting syntax:

$("a.some_div").click(function(){
       //random jQuery code
        return false;
    });

Anyone have any input on this?