oo

As a noun oo is

.

As nouns the difference between o and oo

is that o is a zero used in reading out numbers while oo is the Greek letter omega.

As an interjection o

is the English vocative particle, used before a pronoun or the name of a person or persons to mark direct address.

As a particle O

is The English vocative particle, used for direct address.

As an abbreviation O

is the number of overs bowled.