What does contiguous mean?

Contiguous means adjacent, or continuous without gaps or interruption. A contiguous line is an unbroken line. A contiguous row of bricks is a row of bricks that have been placed adjacent to each other without gaps.

The Contiguous United States means the 48 states that are connected and excludes Hawaii and Alaska.

Similar to states, contiguous counties are counties that share a common boundary and they often span more than one state. However, some are separated by water ways such as lakes or rivers and may not technically "touch" without a gap. That happens when the official county boundaries only extend to the edge of water-way but not to its center. Although not technically contiguous, most still count it as so.