Both retinols and retinoids are a derivative of Vitamin A, a fat-soluble vitamin that's found in everyday household items like carrots and sweet potatoes.
Retinol is a retinoid! - and probably the most popular of the over-the-counter retinoid products. Stronger retinoids such as tretinoin typically require a prescription from a dermatologist.
Since retinol is available over-the-counter, it is less potent than prescription retinoids. In fact, OTC retinoids like retinol typically contain lower concentrations of the active retinoic acid ingredient, starting at .01%.