Definition of o-grade:
(n) :
The name of the Latin-script letter O/o.
(n) :
A zero (used in reading out numbers).
(n) :
(IRC, acronym of) Operator
(n) :
(acronym of) Object, see SVO
(n) :
(uncountable) A blood type that lacks A or B antigens and may only receive transfusions of similar type O blood, but may donate to all (neglecting Rh factor). Synonym: universal donor.
(n) :
An utterance of the vocative O.