Yes, it's the POPM frame:
4.17. Popularimeter
The purpose of this frame is to specify how good an audio file is.
Many interesting applications could be found to this frame such as a
playlist that features better audio files more often than others or
it could be used to profile a person's taste and find other 'good'
files by comparing people's profiles. The frame contains the email
address to the user, one rating byte and a four byte play counter,
intended to be increased with one for every time the file is played.
The email is a terminated string. The rating is 1-255 where 1 is
worst and 255 is best. 0 is unknown. If no personal counter is wanted
it may be omitted. When the counter reaches all one's, one byte is
inserted in front of the counter thus making the counter eight bits
bigger in the same away as the play counter ("PCNT"). There may be
more than one "POPM" frame in each tag, but only one with the same
email address.
<Header for 'Popularimeter', ID: "POPM">
Email to user <text string> $00
Rating $xx
Counter $xx xx xx xx (xx ...)
Been there since ID3v2.3. AFAIK it the the only tag standard with anything about ratings in it.
But ppl have stuffed it up:
M$ use 0 as the lowest rating - not 1;
MM uses 252 as highest rating;
and because users want to use 5-step star or 10-step (with half-stars) ratings, which don't divide nicely into the 1-255 rating, different applications use different points for the changes between steps.
Then add in the de-facto FLAC ratings of 1-100, and you can see why ratings are such a mess.
Personally, I think the granularity of a 255 step rating system is over the top, (put your hand up if you can tell the difference between a not-quite-perfect 254 and a perfect 255
) and a 10-star rating system is plenty.
I just wish someone would take a stand on ratings, across all formats, and stick to it.