Melanesia is a subregion of Oceania extending from New Guinea island in the southwestern Pacific Ocean to the Arafura Sea, and eastward to Fiji. 

The region includes the four countries of Vanuatu, the Solomon Islands, Fiji, and Papua New Guinea.
Besides these independent countries, Melanesia also includes: 

The name "Melanesia" (in French "Mélanésie" from the Greek , "black", and , "islands") was first used by Jules Dumont d'Urville in 1832 to denote an ethnic and geographical grouping of islands whose inhabitants he thought were distinct from those of Micronesia and Polynesia. 

The name "Melanesia" ("islands of dark [people]") is one of several toponyms sharing similar etymologies, ultimately meaning "land of the blacks" or similar meanings, in reference to the dark skin of the inhabitants. The concept among Europeans of Melanesia as a distinct region evolved gradually over time as their expeditions mapped and explored the Pacific. Early European explorers noted the physical differences among groups of Pacific Islanders. In 1756 Charles de Brosses theorized that there was an 'old black race' in the Pacific who were conquered or defeated by the peoples of what is now called Polynesia, whom he distinguished as having lighter skin. In the first half of the nineteenth century Jean Baptiste Bory de Saint-Vincent and Jules Dumont d'Urville identified Melanesians as a distinct racial group.
To label what?
 to denote an ethnic and geographical grouping of islands