Conterminous means to be enclosed within a common border; contiguous means to share a border. Technically, the oft-grouped forty-eight U.S. states should be called the conterminous states, not the contiguous states, since they cannot individually share a border but together are enclosed within a common border. Unfortunately, outside the USGS, the incorrect phrase is far more common and better understood. Use the correct phrase in writing, but—against all my prescriptive wishes—prefer the incorrect phrase in conversation unless you’re ready to explain the difference.