World circles points round radius (7)
I believe the answer is:
tropics
'world circles' is the definition.
(circles around the world)
'points round radius' is the wordplay.
'points' becomes 'topics'.
'round' is an insertion indicator.
'radius' becomes 'r' (abbreviation in geometry).
'topics' going around 'r' is 'TROPICS'.
(Other definitions for tropics that I've seen before include "Region either side of equator" , "hot regions" , "hot spot" , "hot spots" , "heated situations" .)