You use oh when you are hesitating while speaking, for example because you are trying to estimate something, or because you are searching for the right word. I've been here, oh, since the end of June. Zero. the written abbreviation of Ohio
feelings You use oh to express a feeling such as surprise, pain, annoyance, or happiness. `Oh!' Kenny blinked. `Has everyone gone?' Oh, I'm so glad you're here
You use oh to introduce a response or a comment on something that has just been said. `Had you seen the car before?' --- `Oh yes, it was always in the drive.' `You don't understand!' --- `Oh, I think I do, Grace.'
The Single UNIX Specification has historically tried to reduce the number of headers an application has had to include when using a particular interface Sometimes this was fewer than the base standard, and hence a notation is used to flag which headers are optional if you are using a system supporting the XSI extension