LORELAI: I, uh . . . we had one date. It was a great date, World Series level.
The World Series is the annual championship series for Major League Baseball in the US, contested since 1903 and held in the autumn. For this reason it is sometimes called the Fall Classic.
It sometimes confuses people outside the US as to why it is called the World Series when only one nation is involved. One theory is that it was named after the newspaper The New York World, but this is disputed. Most likely it was just a zippy promotional name.