What is the 'Pineapple Express"?

Flip2▶TriviaWORTH ▶
As I noted in this Facebook clip, we are finally having a year-end "rainy season" in Southern California.  Most of the rest of the USA doesn't understand or fully appreciate how much we welcome rain in LaLa Land.  Given our former days in residence around places like Portland, Oregon, (early 70s), we have certainly seen a dearth of moisture for many of the 26 years we have lived in SoCal.

That brings us to the trivial question of our POST title: What is the 'Pineapple Express'?