Species
Definition: A group of living organisms that share common characteristics and can usually interbreed to produce fertile offspring.
In simple words: One particular kind of living thing, such as the tiger or the giant sequoia.
More about species
Defining a species is not always simple — for example, for organisms that reproduce asexually — so biologists use several species concepts. In classification, the species is the basic rank, written with a two-part scientific name such as Panthera tigris.