Biodiversity loss means that all the plants and animals that live on the Earth are disappearing. This can happen because of things like pollution, climate change, or people hunting and catching animals, cutting down forests, and building new cities. All these things can cause animals and plants to die, and when this happens, it makes the planet less diverse, or less biodiverse. This is bad because it means that some species may become extinct, or die off completely and never come back, and we could lose a lot of the plants and animals that make the Earth so special.