You hear the coaches talk about hip hinge is a wide variety of the movements we use in the gym. Here is a definition given by Jake Boly “The hip hinge is a movement pattern that results in the hips shifting back posteriorly causing extension and flexion with a neutral torso.” It can also be described as when the hips are going through a large range of motion when the knees are not.
So essentially hip hinge is when there is maximal hip bend and extension and a squat is when there is both maximal hip bend and also maximal knee bend.
Hip hinge is seen is jumping, kettlebell swings, good mornings, deadlifts, high hang and hang clean, high hang and hang snatch to name a few. This is when you have a soft knee (not a drastic knee bend) and use your hips for power. Some sports specific movements where you can see this is in the baseball swing stance, basketball shooting stance, golf swing, and skating in hockey to name a few.