In biology, a species is smallest and basic unit of classification. Each species is placed within a single genus. For example biological name of human being is homosapiens. Here homo is the genus and sapiens is the species of humans.

Earlier species was thought to be an indivisible, stable unit but in modern taxonomy subdivisions of species, such as sub species have been created which help in our understanding of classification.

Definition of species

According to ernst mayr"a species is a group of fertile organism that can interbred and produce fertile offspring of both the gender".

The modern concept considers species as a group of actually or potentially inter breeding natural population of closely resembling individuals.  Species can also be defined on the basis of various perspectives, which are as follows.

Morphological: a population or group of population that differ morphologically from each other eg. Chicken-duck.

Biological: a set of actually or potentially inter breeding populations or two organisms that are able to reproduce naturally to produce  fertile offspring of both the genders.

Ecological:  a set of organism adapted to particular set of resources, called a niche, in environment.

Genetic: based on similarity of DNA of individuals or populations.