Strictly speaking, a play mat is just the foam or cloth surface you lay on the ground. It is designed to be visually stimulating for a baby. A play gym is the mat plus an overarching system of dangling toys or toys attached to other parts of the mat. Play gyms will encourage babies or toddlers to work their developing muscles by reaching or kicking toys. An activity mat is a fabric mat with animals or flowers sewn into it that may squeak or crinkle or provide other sensory experiences other than sight.