Cascadia's a Place, a Bioregion known better as the Pacific Northwest. Cool wet air travels thousands of miles over the ocean and the Arctic and crashes in to the Cascade Mountain Range and dumps cool wet rain for thousands of years.
In 2019, I went on a Westfalia Vanagon Trip around the northern olympic and cascade regions and was glad to experience the luscious, damp wet, Hoh Rain Forest out to the eastern slopes of the Cascades where ferns turn to sage and there's signs warning you for rattlesnakes.
The region is temperate, cool, and gets plenty of rain. Some folks say it's too much, but I love the cold grey, I dream of those foggy days on the sound. Maple trees grow here and other trees show beautiful color in the fall, I can grow Tea1 and keep a garden. There is plenty of fauna and flora, and a lot of diversity.
It's not a perfect place or a perfect signifier: for many Cascadia is a secessionary dogwhistle or the call to anti-federalism in the hills of rural Oregon and in the Washington State House.