Poor is the highest of the three failing grades, out of six grades overall, in the Ordinary Wizarding Levels, Nastily Exhausting Wizarding Tests and Wizards' Ordinary Magic and Basic Aptitude Tests. It is the third lowest mark, immediately below Acceptable and immediately above Dreadful.
Entering into N.E.W.T. Classes
If a student receives a Poor (or lower) on an O.W.L. for a particular subject, the student has failed that subject and is unable to continue on with it as a N.E.W.T. class.