A species is a distinct group of animals or plants that have common characteristics and can breed with each other. Your poodle and your bulldog are the same species, but your hamster and your goldfish are not.
All members of the same species have similar genes and can interbreed and produce offspring. A subspecies is a division of a species, and a genus includes several different species. Biologists use these categories to classify organisms, usually with Latin names like Canis familiaris, or "domestic dog." In Middle English, species meant "a classification in logic," borrowed from the Latin word meaning "kind or appearance," from the root of specere, "to see."