A pang is a sharp jab or an intense hurt that comes on suddenly. If you've felt an all-of-a-sudden, deep sadness that seems to hit you even in the back of the eyes, you've probably had a pang of emotion over a loss or a tragic story.
You can feel a physical pain or pang right when you get hurt, or you might suffer a pang of guilt that keeps popping up if you don't own up to something bad. Pang sounds close to pain, and it is pain, but it has a sharper edge — it's intense and comes on fast. A childbirth pain often is called a pang, because it's such a unique type of hurting. Having a pang of regret can be almost as sharp.