Extraordinary in alien territory? (3,2,4,5)

I believe the answer is:

out of this world

I'm a little stuck... Click here to teach me more about this clue!

'extraordinary' is the definition.
(I've seen this in another clue)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for out of this world that I've seen before include "Delightful" , "ET was" , "Are stars so" , "worth waiting for" , "astronauts fired here" .)

I've seen this clue in The Telegraph.

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