This is it!

this is it

1. This is the key moment that we have been waiting for or anticipating. OK, everyone, this is it—if we win this game, we'll be in the championships.
2. This is the place or thing that I need or have been waiting for. A: "Is this the book you need?" B: "Yes, this is it, thank you so much for helping me find it!"
3. This is the point that sums everything up. A: "The only way we can start to address this problem is to prioritize building new, affordable housing." B: "Yes, this is it. Any other measures, even if necessary, won't help the crisis as it exists right now."
See also: this

This is it!

1. exclam. This is exactly what I have been looking for!; I have found it! This is it! The world’s best pizza!
2. exclam. This is the crucial moment! Get ready, this is it! Jump now!
See also: this