Great gallery means to project information (7)
I believe the answer is:
acetate
'to project information' is the definition.
I can't judge whether this definition defines the answer.
'great gallery' is the wordplay.
'great' becomes 'ace' (ace can informally mean very good).
'gallery' becomes 'tate' (Tate Modern, Tate Britain etc).
'ace'+'tate'='ACETATE'
'means' acts as a link.
Can you help me to learn more?
(Other definitions for acetate that I've seen before include "Transparency used with an overhead projector" , "It once covered records" , "film on overhead projector" , "(Chemical used in production of) clear film" , "Material in old record" .)