Artifact Lands are a combination of artifact and land and are subject to the rules for both. They were very useful in the Affinity-based decks, but they are now banned in Mirrodin Block.
212.2f - Artifact lands combine the characteristics of both lands and artifacts, and are subject to spells and abilities that affect either or both card types. Artifact lands can only be played as lands. They can't be played as spells.