if (d) {some code} what does it mean?

does it mean that in case d is true then {some code} or what?
i simply don't know...
thanks for checking this post out.

 

i'm sure it means if variable is active or has data in it (i stand to be corrected)?
eg:

<script type="text/javascript">
<!--
function confirmation() {
	var answer = confirm("Leave digitalpoint.com?")
	if (answer){
		alert("Bye bye!")
		window.location = "http://www.google.com/";
	}
	else{
		alert("Thanks for sticking around!")
	}
}
//-->
</script>

Code (markup):

 

thanks man. now i understand!