What is the difference between rotator cuff tear and impingement?

RC: Impingement implies a pinching of the rotator cuff generally underneath the bone called the acromion. This is often associated with either a bone spur or a curved acromion. This can in some situations lead to a tear of the rotator cuff. Rotator cuff tears imply an actual rip in one or more of the tendons. Most often the tear is from the attachment site of the tendon to the bone.

Intact vs. nonintact: Impingement means that the rotator cuff is intact, but inflammed or impinged by the bony architecture of the shoulder. A rotator cuff tear is, obviously, when the rotator cuff tendon(s) are torn away from their bony insertion.