Funafuti is an atoll

Atoll

An atoll is a coral island that encircles a lagoon partially or completely.- Usage :The word atoll comes from the Dhivehi word atholhu OED...

 that forms the capital of the island nation

Island nation

An island country is a state whose primary territory consists of one or more islands or parts of islands. As of 2011, 47 of the 193 UN member states are island countries.-Politics:...

 of Tuvalu

Tuvalu

Tuvalu , formerly known as the Ellice Islands, is a Polynesian island nation located in the Pacific Ocean, midway between Hawaii and Australia. Its nearest neighbours are Kiribati, Nauru, Samoa and Fiji. It comprises four reef islands and five true atolls...

. It has a population

Population

A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...

 of 4,492 (2002 Census), making it the most populated atoll in the country

Country

A country is a region legally identified as a distinct entity in political geography. A country may be an independent sovereign state or one that is occupied by another state, as a non-sovereign or formerly sovereign political division, or a geographic region associated with a previously...

. It is a narrow sweep of land between 20 and 400 metres wide, encircling a large lagoon 18 km long and 14 km wide, with a surface of 275 km², by far the largest lagoon in Tuvalu. The land area of the 33 islets aggregates to 2.4 km², less than one percent of the total area of the atoll.