What does it mean to play in a key?

[rischoll]

So what does it mean to play in a key...?

What chords correlate to which keys and how does it all fit together...?

How does this all relate to soloing and improvisation?

[Danny Poole]

So what does it mean to play in a key...?

In short when you play in a certain key you are playing a group of notes and chords that go together. Read more about key signatures here!

What chords correlate to which keys and how does it all fit together...?

Just the same way there is a major scale for notes (in any key) there is also a scale for chords (in any key). Read more about Chord Key Relations here!

How does this all relate to soloing and improvisation?

Read this thread to help with improvising http://www.guitartutoronline.com/for...read.php?t=119