I had no idea there was a Plymouth Rock breed of chickens or that barred was a color. See how educational this blog is…well, for me anyway.

From Wikipedia:
The Plymouth Rock, often called simply Rocks or Barred Rocks (after their most popular color), is a chicken breed that originated in the United States. The Plymouth Rock is a dual-purpose, cold-hardy bird and therefore makes a great breed for the small farm or backyard flock owner. The Barred Rock is often called the Plymouth Rock, but this title correctly belongs to the entire breed, not just the Barred variety.