Bio active means creating a miniaturised ecosystem to the best of our ability within the confines of an enclosure. This is achieved by structuring the substrate to accommodate live plants, along with the introduction of microfauna (Worms, isopods like woodlice, springtails etc) often referred to as custodians. These act as a miniaturised clean-up crew to turn over the soil, break down waste and recycle nutrients for the plants to utilise for growth. Enclosures like this often require additional lighting to promote healthy plant growth and people often add automated misting or humidifying systems to help control the humidity within the environment. Bioactive enclosures are a similar concept to a fish tank, in a fish tank the filter contains millions of bacteria to break down waste and keep the water quality safe. In a bioactive reptile or amphibian enclosure this job is performed at least in part by the custodians.

Does that mean I never have to clean my enclosure?

No, this is one of the most common mistakes people make when assuming bioactive enclosures are a perfect environment. Remember they are still a closed ecosystem and in the same way that you have to perform water changes on a fishtank you will from time to time need to remove and replace some of the substrate, add additional custodians and trim plants.