AAA on Yoshi's Cookie
An AAA (triple A) or a perfect score, is achieved when you hit every arrow in a chart with a 'perfect' result. You will also receive rank 1 on that song, match the FFR best and in theory, will never have to play that song again.
A sightread AAA on Big Blue v2
Additionally, a sightread AAA is a perfect score on the first time a player has ever played it, as hinted by a best rank of 0.