Celebration, finding a grid layout inside planet (5,4)
I believe the answer is:
mardi gras
'celebration' is the definition.
(Mardi Gras is an example)
'a grid layout inside planet' is the wordplay.
'layout' indicates anagramming the letters (an alternative layout of the letters).
'inside' is an insertion indicator.
'planet' becomes 'mars' (Mars is a planet).
'a'+'grid'='agrid'
'agrid' anagrammed gives 'digra'.
'digra' going inside 'mars' is 'MARDI GRAS'.
'finding' acts as a link.
(Other definitions for mardi gras that I've seen before include "Shrove Tuesday festival" , "Revelry celebrating Shrove Tuesday" , "Shrove Tuesday celebration" , "Day for 9 acrosses" , "Time for carnival" .)