Perfect concept on laptop (5)
I believe the answer is:
ideal
'perfect' is the definition.
(similar in meaning)
'concept on laptop' is the wordplay.
'concept' becomes 'idea' (I've seen this before).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'laptop' becomes 'l' (top of the word 'lap').
'idea'+'l'='IDEAL'
(Other definitions for ideal that I've seen before include "Perfect but not likely to become a reality" , "(the best one can get)" , "Optimal" , "Paragon" , "Pattern" .)