An activity gym may be a soft mat on that a baby will lie down And over them is an arch that has varied attachments, like lights, toys, balls, varied colorful objects, rattlers, tethers et al. Also, on most models there are partaking activities on the mat itself, like mirrors. Most additionally come with sounds, like music and animal sounds, a number of that are activated by the baby.
Source: http://omgstroller.com/best-baby-gym-reviews/