Genus comprises a group of related species which has more characters in common in comparison to species of other genera.
We can say that genera are aggregates of closely related species. For example, potato, tomato and brinjal are three different species but all belong to the genus Solanum.
Lion (Panthera leo), leopard (P pardus) and tiger (P. Tigris) with several common features, are all species of the genus Panthera. This genus differs from another genus Fells which includes cats.