I will quote directly from wikipedia, "a strong and persistent flow of atmospheric moisture and associated heavy rainfall from the waters adjacent to the Hawaiian Islands and extending to any location along the Pacific coast of North America."

Pretty much we are hit with heavy rain that leads to some flooding. (which is a problem in my neighborhood due to drainage) We are in the midst of an El Nino winter so we are getting more rain and snow. A real bother to put up with in the winter BUT the upside is that we will have enough water in our reservoirs that drought won't be an issue in the Summer.

We are weather nerds in this part of the world.