Engineer claims idea involving old interactive websites (6,5)
I believe the answer is:
social media
'interactive websites' is the definition.
(websites allowing social interaction online)
'engineer claims idea involving old' is the wordplay.
'engineer' is an anagram indicator.
'involving' means one lot of letters goes inside another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'claims'+'idea'='claimsidea'
'claimsidea' anagrammed gives 'scialmedia'.
'scialmedia' enclosing 'o' is 'SOCIAL MEDIA'.
(Other definitions for social media that I've seen before include "Apps used for networking" , "Popular communications channels" .)