A Flip effect (リバース効果 Ribāsu Kōka "Reverse Effect"), formatted Flip Effect prior to the version 9.0 TCG rulebook, is a kind of Trigger Effect possessed exclusively by Flip monsters. This kind of effect activates when the Flip monster is flipped face-up (by battle, a Flip Summon, or a card effect). In card text, Flip effect is marked with the all-caps text "FLIP: ".
If the monster is flipped up and destroyed by battle, the card is destroyed first, then its effect is activated and resolved on the field in the Damage Step after damage calculation; since the card is already destroyed, effects like that of "Hane-Hane" cannot target themselves.
Not all monsters with effects that activate upon flipping face-up are Flip monsters; some monsters have Pseudo-Flip Effects, which function identically to Flip effects other than the monsters not being considered Flip monsters (so their effects can activate if flipped by cards like "Ceasefire"). In addition, not all Flip monsters' have effects that trigger upon being flipped face-up, such as "Worm Linx" and "Aroma Jar".
Previously, Flip Effects were considered a distinct kind of effect from Trigger Effects, and several card effects specifically affected Flip Effects; such cards now instead affect all effects of Flip monsters.
In Yu-Gi-Oh! The Duelists of the Roses, a Flip Effect is a one-time effect that is activated only when the card is manually flipped face-up or as a result of another event, such as battle.