Pelvic tilt refers to the position of your pelvis in the three planes of motion. Posterior and Anterior tilt refer to the position in the sagittal plane. If the top of the pelvis tends to tilt down towards the front of the body, causing the buttock to stick out, this is an anterior tilt. The opposite, with the top of the pelvis tilting towards the rear and bringing the tailbone under the body, is called posterior tilt.
Excessive anterior or posterior tilt (more often anterior) can interfere with proper posture and lower body mechanics, particularly in movements like the squat and deadlift. The tilt is often the product of tight or inhibited muscles, although it can have many causes.
The pelvis can also tilt in the frontal and transverse planes causing ‘hip hikes’ or a rotated lower spine.