Hints for words that begin with an apostrophe unfortunately do not work yet -- it's a known problem that developers have on their list but I don't know when it will be fixed.
'oH is a personal pronoun that means "it" -- it refers to one thing that cannot use language (for example, animals or inanimate objects). For example, 'oH vIlegh. "I see it."
Since Klingon doesn't have a verb meaning "to be", pronouns are used in that sort of situation, so 'oH may also be translated as "it is" or "is" depending on the sentence, e.g. raS 'oH "it is a table" or torgh 'oH pongDaj'e' "his name is Torg".