The type that is found in glasses (7)
I believe the answer is:
species
'the type' is the definition.
(I've seen this before)
'that is found in glasses' is the wordplay.
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
'found in' is an insertion indicator.
'glasses' becomes 'specs' ('specs' can be a synonym of 'glasses').
'ie' placed inside 'specs' is 'SPECIES'.
(Other definitions for species that I've seen before include "Sort, type" , "Kind of creature" , "Taxonomic group whose members can interbreed" , "Breed or genus" , "Variety, taxonomic group" .)