"This is it" can be used in multiple ways. 1.) It can be said when you reveal something to someone For example: Person 1 "we're here" Person 2 "this is what you wanted to show me?" Person 1 "yes, this is it!" 2.) It can also be said when something is about to happen (mostly the end of something) or about to be revealed. For example: (Imagine people being chased by monsters and when the monster are nearby and approaching) Person 1 "This is it...isn't it?" Person 2 "...yeh, it was nice knowing you mate" Addendum: Make sure you don't get this mixed up with "that is it." "That is it" is mostly used when someone has had enough of something. For example: *people arguing* Person 1 "THAT IS IT...I CAN'T TAKE THIS ANY MORE!" Additional: "This is it" is a name of an concert performance from the famous pop artist Michael Jackson. The reason he called it that was because it was his last set of performances he would ever do.

That is " it". all about it. All set, no more,that is end,nothing more....Often after sneezing.

THIS IS the time, the place, the opportunity, the thing, the color of the sky (whatever you want) we waited for or we've been looking for, we finally found it !!! ... this is it ! ^^

It is the same to say THIS IS A BALL... or, THIS IS A PEN !