Every recognized species on earth (at least in theory) is given a two-part scientific name. This system is called "binomial nomenclature." These names are important because they allow people throughout the world to communicate unambiguously about animal species. This works because there are sets of international rules about how to name animals and zoologists try to avoid naming the same thing more than once, though this does sometimes happen. These naming rules mean that every scientific name is unique. For example, if bluegill sunfish are given the scientific name Lepomis macrochirus, no other animal species can be given the same name. So, if you are a Russian scientist studying relatives of sunfish and you want to discuss bluegill sunfish with a Canadian researcher, you both use the scientific name and know exactly what the other is talking about.
Scientific names are also designed to tell you something about the animal's relationships with other animals. The scientific name of each species is made up of a generic name (generic epithet) and a specific name (specific epithet). In our bluegill sunfish example the generic epithet is Lepomis and the specific epithet is macrochirus. The generic epithet is the name of the genus (singular of genera) to which bluegill sunfish belong, the genus Lepomis. Some genera contain only one species but most genera are made up of many species. There are other species of sunfish in the genus Lepomis, examples are Lepomis cyanellus (green sunfish), Lepomis megalotis (longear sunfish), and Lepomis gibbosus (pumpkinseed sunfish). Notice that all of these species share the same generic epithet, this indicates that they are all thought to be more closely related to each other than to any other species of fish. The genus is the first level of taxonomic organization, in a way, because all species that are thought to be most closely related, are placed together in a genus.
Scientific names are often descriptive also, suggesting something about the animal. For instance, longear sunfishes have long and conspicuous operculum flaps (a hardened structure extending from the gill flap), making them look like they have long ears. The specific name, megalotis, means "big ears." Another example is yellow-headed blackbirds, whose scientific name is Xanthocephalus xanthocephalus, which literally means "yellow-headed, yellow head." Scientific names also sometimes bear the names of people who were instrumental in discovering or describing the species. Myotis keenii, "Keen's mouse-eared bat", is named after a gentleman named Keen (Myotis means "mouse-eared"). They may also contain references to regions where the species are found, such as southern right whales, Eubalaena australis, which translates to "southern true-baleen." Finally, some scientific names reflect the common names given to these animals by native peoples, such as Oncifelis guigna, a small, South American cat species called guigna by people of Chile and Argentina.
Unlike scientific names, common names are not unique. As a result, common name usage can lead to confusion about what animal is being referred to and what their relationships are to other animals. An example are "badgers." There are various animals worldwide that are superficially similar, honey badgers (Mellivora capensis), North American badgers (Taxidea taxus), Eurasian badgers (Meles meles), stink badgers (Mydaus javanensis), and ferret badgers (Melogale personata). Although they are all called "badgers" and they are all members of the same mammalian family, they are not each other's closest relatives.
There are many examples of confusing and redundant common names, just remember that you can't rely on the common name to tell you anything about the animal's evolutionary history.
Taxonomy, the science and process of naming living organisms, is a field that is constantly changing. When our scientific understanding of animal species and their relationships changes, it may mean that scientific names change as well. For example, all small cat species were once included in the genus Felis. They have since been split into multiple genera in order to better represent important evolutionary differences among them. Bobcats were once known by the scientific name, Felis rufus, this name has since been changed to Lynx rufus. Unfortunately, older scientific literature on bobcats will still be found under Felis rufus and some sources may not recognize the name change right away.
Some species have come to be known by multiple scientific names. In such cases one name is chosen for the species and the other names are referred to as "synonyms" of the species name. For example, all bats in the genus Lasiurus were once also known by the generic name Nycteris. So Lasiurus borealis would have also been known as Nycteris borealis. The valid, currently recognized name is Lasiurus borealis and Nycteris borealis is considered a synonym.
If you cannot find information for a particular scientific name try searching the taxonomy databases we use, to be sure that the species isn't known by a different name.