Learner surrounded by mediocre talent (5)
I believe the answer is:
flair
'talent' is the definition.
(flair is a kind of talent)
'learner surrounded by mediocre' is the wordplay.
'learner' becomes 'l'.
'surrounded by' indicates putting letters inside.
'mediocre' becomes 'fair' ('fair' can be a synonym of 'mediocre').
'l' placed inside 'fair' is 'FLAIR'.
(Other definitions for flair that I've seen before include "Style, panache" , "Intuitive discernment" , "Natural ability/talent" , "Taste" , "Stylishness; talent" .)