Beginner: This is so basic a level that it’s not usually included in the levels. Maybe just the meloly in the right hand.
Easy
Elementary: Still easy, but usually making use of both hands. Very few chords.
Late Elementary: Introduction of chords in the left hand.
Moderate: Here’s where it changes from, say, block chords in the left hand to slow arpeggios.
Medium
Early Intermediate: Faster arpeggios. More complex chords.
Intermediate: This is this as your typical church pianist. Most of my “stride” arrangements will land here.
Late Intermediate: Playable, but definitely needing some practice time. This is probably sight-readable, but only after some prep time.
Difficult
Early Advanced: Still playable, but needing more practice time. Usually requires some quality time to get familiar with the music.
Advanced: If I find it hard to play, this is where it will end up. This is the most difficult category I’ll use on a regular basis.
Impossible: Just what it says. I may add a verse here and there that, while in theory could make sense, it is practically unplayable.