212.6d.

The basic land types are Plains, Island, Swamp, Mountain, and Forest. If an object uses the words "basic land type," it's referring to one of these subtypes. A land with a basic land type has an intrinsic ability to produce colored mana. (See rule 406, "Mana Abilities.") The land is treated as if its text box included, "{T}: Add [mana symbol] to your mana pool," even if the text box doesn't actually contain text or the card has no text box. Plains produce white mana; Islands, blue; Swamps, black; Mountains, red; and Forests, green.