What's the difference between 3-finger mittens and trigger mitts?

The terms are often used interchangeably, but technically, 3-finger (or lobster claw) designs have a more defined index finger compartment similar to a glove finger, while trigger mitts have a more mitten-like construction with an articulated index finger pocket that's less separated from the main chamber. Trigger mitts lean slightly warmer with less dexterity; 3-finger designs lean slightly more dexterous with a bit less warmth. In practice, the difference is small and most skiers won't notice a dramatic difference between the two.