Trigger Finger is when a flexor tendon, which bends your finger, becomes stuck in a pulley in the palm of your hand. This can be like trying to pull a piece of string with a knot in it through a straw, it will get stuck and then suddenly give way allowing further movement.
Sometimes, the tendon becomes swollen or the pulley becomes tight: this may result in triggering of the finger. Some people have a tendency for multiple fingers to trigger at different times. This is more common as we age and in people with diabetes1. Triggering of the finger is often worse in the mornings and can be noted on waking.