A flipper tab is a small lever on the back of the blade that protrudes from the spine of the handle when the knife is closed. Pull it with your index finger and the blade swings open. It is the fastest one-handed opening method that involves no springs.
The tab is simply the rear of the blade extended past the pivot. Pulling it applies leverage that overcomes the detent, and once the detent releases, the blade’s own momentum carries it to the stop pin.
Nothing stores energy. That is the important legal and mechanical distinction between a flipper and a spring-driven opener: the blade only moves because your finger moved it.
A crisp flipper needs three things in balance: a strong enough detent to store the resistance, a smooth pivot on bearings or washers, and a tab shaped so your finger does not slip. Get one wrong and the action feels mushy.
Once open, the tab usually becomes a small guard in front of your index finger, which is a genuine safety benefit.