A "destination wedding" is where the entire wedding takes place at some exotic location. One of my co-workers just got married in Mexico.
Unlike a traditional wedding in your hometown, where all the family and friends come (which can be 100 people and up) in a destination wedding only the wedding party and special guests usually attend. Because most people aren't going to shell out thousands of dollars to go to Mexico for a cousin's or co-worker's wedding.
So the "affair" is small.