In short
Binomial nomenclature is the scientific system of giving each species a two-part Latin name: the genus name first, then the species name. It was introduced by Carl Linnaeus.
The first word is the genus and always starts with a capital letter. The second is the species and starts with a small letter. The whole name is written in italics, or underlined by hand. Every species has just one scientific name, used all over the world, so scientists avoid the confusion of common names that vary from place to place.
Humans are Homo sapiens: genus Homo, species sapiens. The mango is Mangifera indica, and the tiger is Panthera tigris.
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