Acceptable

"We are pleased to tell you that you have passed your Grade 1 W.O.M.B.A.T. Your knowledge of the workings of the wizarding world demonstrates real magical potential."

— 'Acceptable'-graded W.O.M.B.A.T.^[src]

Acceptable^[1] is one of the three passing grades, and one 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 highest mark and lowest passing grade, immediately below 'Exceeds Expectations' and immediately above 'Poor'.

Advancement

"I'm sorry, Longbottom, but 'Acceptable' really isn't good enough for N.E.W.T. level. I just don't think you'd be able to cope with the coursework."

— The increased difficulty in course work^[src]

As 'Acceptable' is a passing grade, the student might be able to enter into the N.E.W.T. class that they passed in. However, some teachers, like Severus Snape, only allowed students with an 'Outstanding' grade to enter his N.E.W.T. classes. Additionally, Minerva McGonagall refused to accept Neville Longbottom into her N.E.W.T.-level Transfiguration class with only an 'Acceptable' on his Ordinary Wizarding Level. This may indicate that students who receive only an 'Acceptable' O.W.L. for a subject might not routinely be allowed to continue at N.E.W.T.-level, as Professor McGonagall believed that Neville would not be able to cope with the course load.^[2] It is therefore also likely that, given that a student has already passed a subject with an 'Acceptable' grade, that the student could not retake that subject.