>>127280980
key can be any note from A to G sharp or whatever. key just tells you what chords will be where in relation to the key center (see pic). most blues are a 1-4-5 progression. so if i play a blues in the key of G, my 4 will always be C and my 5 will always be 5. it's just a roadmap to explain things more quickly. the chord progressions also line up with the respect major/minor scale intervals of the key center. intervalic distances and by extension chord progressions will generally have the same feel regardless of key center. that's why similar chord progressions and scales largely feel the same despite being in different keys