There are two separate defitions. Definition 1: Preparatory position of all 4's (hands & knees), start position is to draw one knee into your chest. Exercise is done to slowish pace 4-count and then repeated for the other leg. First, extend leg straight out to the rear, parallel to spine; second, swing leg out as wide as possible; third, bring leg back to straight behind, parallel with spine; fourth, bring knee back to chest. Enough of these will have abs & glutes feeling the burn. Variation for the bold: do from side plank position. Definition two: From low-plank position, touch right hip to ground, then back to center. Touch left hip to ground, back to center. Down in four-count cadence.