Gabrielle Tillman says:
T.A. Tilley is right...traditionally a treatment is a VERY detailed account of everything that happens in each scene of a movie - beat by beat, minus dialogue. It may seem unfathomable, but in the past treatments have actually been over a HUNDRED pages, and they can even run longer than the script itself because a treatment should include subtext and characters thoughts, neither of which can show up in an actual draft since it's mainly the territory of the actor. Contemporarily speaking, however, the word 'treatment' has been extended to include short and long form outlines. It really depends on who your speaking with, but people who have been in the industry longer (30, 40 plus years) still tend to use the term 'treatment' in the way it was originally intended.