Frontierland is a recreation of the old west in America, and was one of the original five "lands" at Disneyland. Frontierland has changed drastically from its Mule Ride and "Living Desert" days. It is usually one of the least populated lands in the park, and is usually used as a walkway to other parts of the park.
Tips:
During and after Fantasmic!, Frontierland is used as an entry way into the West side of the park. Guests will be escorted along a clearly marked route and must follow this pathway. If you are using Frontierland to get to New Orleans Square or Critter Country during this time you'll be in for a wait. Do not try to go through Adventureland though. You will just be told to walk through Frontierland