"Parallel squats" refers to a type of exercise where you bend your knees and lower your body down to a position where your thighs are parallel to the ground. Full definition
However, some people will never be able to perform a deep squat with good form because of pelvic anatomic limitations, while others who have knee issues such as chondromalacia, arthritis or torn menisci will be better off with parallel squats because the increased ptellofemoral and tibiofemoral compression involved in deep squatting can worsen their condition. (fitnessandpower.com)
Athletes must do parallel squats in order to achieve the ultimate activation of the quads and gluteus. (fitnessandpower.com)
Performing parallel squats is still a million times better than not squatting at all and it will definitely increase your mass and strength gains, so don't beat yourself up and make the most use of the exercise. (fitnessandpower.com)