There exist two types of targeting systems in terms of combat: One is called “hard aim” and the other, “soft aim.”
Hard aim is the use of your reticle to determine precisely where your gunshots fire. Although attacks that use this aim type require accuracy on the user’s end, they come with the bonus of enabling critical hits (hitting enemy weak points). All guns use hard-aim targeting. The biotic power Lance is unique to other powers since it uses hard-aim targeting. As such, it can inflict critical damage.
Soft aim is a lock-on mechanism used by most enemy-targeting powers. Your soft-aim target is represented by a surrounding bracketed rectangular reticle. Powers using this aim type do not require as much accuracy, as the power seeks outs its target. However, soft aim does not make the power guaranteed, as obstacles between you and your target can still block certain projectile powers.