Cascadia is a term that means many things to different people.

Firstly, it is a bioregion that defines the Pacific Northwest of the United States and Canada, incorporating British Columbia, Washington, Oregon, parts of Idaho, southern Alaska and northern California, and in many ways is geographically, culturally, economically and environmentally distinct from surrounding regions. It is a place in the world with unique flora and fauna, topography, geology and is comprised of a interconnected ecosystems and watersheds.

Cascadia is also a growing social and cultural movement. It is used to define a unique regional character found within the Pacific Northwest, and extends to a wide range of beers (Cascadia Dark Ale), sports (the Cascadia Cup) and music (Cascadian Black Metal) just to name a few. The idea has since been adopted by a wide range of researchers who highlight the growing importance of regional growth management, environmental planning, economic cooperation, as well as disaster preparedness. Support for the idea also comes from institutions and businesses such as the Bullit Foundations 'Cascadia Center', the adoption of the Cascadia Megaregion by federal policy makers, and the tectonic Cascadia Subduction Zone.

Cascadia is also a slowly emerging independence movement. It has been listed #7 on Time Magazines top 10 most likely to succeed (at seceding) independence movements, along with Tibet, Scotland and Catalonia, as well as listed as Vice Magazines personal favorite independence movement, along with being featured in a wide range of publications, such as the NYtimes, CNN, Forbes, Portland Monthly, the Seattle Times, the Wall Street Journal, the Oregonian and many others.

 A much more common definition of Cascadia instead seeks simply to help further local autonomy, empower individuals and communities to better represent their own needs, as well as push or environmental and economic responsibility, and increased dynamic, transparent and open governance. The Cascadia movement encourages people to reengage with their local communities, develop local and personal resilience (community gardens, disaster preparedness, etc.), and create alternate lines of regional communication, politics, and interdependence that better represent the social, cultural and political boundaries that define our region.

The term Cascadia was adopted in 1970 by Seattle University professor David McCloskey, as a way to better describe our growing regional identity. McCloskey describes Cascadia as "a land of falling waters." He notes the blending of the natural integrity and the sociocultural unity that gives Cascadia its character. Definitions of the region's boundaries vary, but usually include the area between the Cascade Range and the Pacific Ocean, and some part of the Coast Mountains. Other definitions follow the boundaries of existing subnational entities, and usually include the territory of British Columbia, Washington, and Oregon, while others also include parts of California, Idaho, Alaska and Yukon.

In general, the area in and around the Cascadia region is more commonly referred to as the Pacific Northwest. The area's biomes and ecoregions are distinct from surrounding areas. The resource-rich Salish Sea (or Georgia Basin) is shared between British Columbia and Washington, and the Pacific temperate rain forests, comprising the world's largest temperate rain forest zone, stretch along the coast from Alaska to California.