A species is a group of organisms that can interbreed and produce fertile offspring in the natural environment. In other words, members of a species share a common gene pool and are capable of exchanging genetic material through reproduction.

Species can be categorized into different taxonomic groups based on their genetic similarities and evolutionary relationships. For example, organisms that belong to the same genus (plural genera) are more closely related to each other than those that belong to different genera. Organisms that belong to the same family (plural families) are more closely related to each other than those that belong to different families, and so on up the taxonomic hierarchy.