PUERTO RICO (March 2012)
Years ago I gave an assignment to a basic mathematics course I was teaching that involved finding what fraction of US states satisfied certain criteria, such as what fraction of states begins with M. I figured at least the denominator of these fractions would be easy as everyone knows there are 50 US states. One student turned in her assignment with all of her fractions written over 51. I asked her what the 51st state was and she replied, "Puerto Rico."
In fact, Puerto Rico is not a state but a US Commonwealth, a type of organized but unincorporated dependent territory. In all there are five inhabited terriroties under the United States (American Somoa, Guam, Nothern Mariana Islands, and the US Virgin Islands form the others), each with varying statuses of being organized or unorganized. As a Commonwealth, a US citizen does not require a passport to travel to Puerto Rico, which is convenient.
Located in the northeastern Caribbean, Puerto Rico is east of the Dominican Republic and west of the US Virgin Islands. Getting there for us requires flying from LAX to JFK and then on to San Juan (we'll be flying through Miami upon our return).