Where conterminous means to be enclosed within a common border, contiguous means to share a border. Technically, the oft-grouped U.S. states should be referred to as the forty-eight conterminous states, not the forty-eight contiguous states—they cannot each share a border, but together they share a common border. Unfortunately, outside the USGS, the incorrect phrase is far more common and more readily understood. Use the correct phrase in writing, but—against all my pedantic wishes—prefer the incorrect phrase in conversation unless you wish to raise most eyebrows in the room.