Octogenarians resisting strong treatment in this region (7)

I believe the answer is:

oceania

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

'this region' is the definition.
(region of Earth)

I can't explain the rest of the clue.

(Other definitions for oceania that I've seen before include "Islands of the central and South Pacific" , "Islands of Pacific and adjacent seas" , "Pacific islands region" , "remote area" , "Islands of the south Pacific -- a neo-CIA (anag)" .)

I've seen this clue in The Irish Times.

Want a hint initially instead of a full solution? Install my app