Full Idea
The concept of qualia (a part of the folk concept) is the concept of properties of experiences apt for causing abilities to recognize and to imagine experiences of the same type.
Gist of Idea
Part of the folk concept of qualia is what makes recognition and comparison possible
Source
David Lewis (Should a materialist believe in qualia? [1995], p.327)
Book Reference
Lewis,David: 'Papers in Metaphysics and Epistemology' [CUP 1999], p.327
A Reaction
I presume the other part of the folk concept would be what it is about qualia that makes this possible, namely that they 'look/sound/feel.. the same'. Lewis emphasises the functional aspect, which could not possibly be the whole story.