Biodiversity is the variety of different living things in a particular place. A forest with dozens of tree species, hundreds of insects, birds, mammals, fungi, and plants has high biodiversity. A lawn with just grass and a few dandelions has low biodiversity.

The word combines “bio” (life) and “diversity” (variety), and scientists use it to measure the health of ecosystems. Think of biodiversity like the difference between a cafeteria offering fifty menu choices versus one offering only three: more options mean the system works better when something goes wrong. If disease wipes out one tree species in a diverse forest, dozens of others survive. If disease hits the only tree species in a plantation, the entire forest can collapse.

Coral reefs have incredible biodiversity, packed with thousands of species in a small area. Rainforests too. Even your backyard has biodiversity: earthworms, beetles, spiders, birds, squirrels, bacteria in the soil, and countless plants all playing different roles.

When people talk about protecting biodiversity, they mean preserving these rich, complex communities of life. Scientists worry when biodiversity drops because it usually means ecosystems are becoming fragile. A lake losing half its fish species, or a meadow where butterflies disappear, signals that something has gone wrong with that environment's ability to support diverse life.