Collider2D and Z-Axis

Just to make sure:

Collider2D will never consider z axis, right? in other words if i have a background in z axis = 10 and an object in z axis -10, both with theirs colliders and rigidbodies... so collision will be detected once they touch in X and Y axis only. Z axis doesnt matter...

Is that concept right? My point is: My "bullets" are colliding/triggering against my background and other objects, which is not same Z-Axis that themselvies before they collide with characters in the game...

Yes, it is a 2D game...

I wait for any comments.