Apart from its use as the name of a mark of punctuation ('), the term apostrophe is used for a kind of formal invocation. Sometimes the invocation is to an absent (or even dead) person: "Milton," writes Wordsworth, "thou shouldst be living at this hour;/ England hath need of thee." At other times, an inanimate object can be invoked: "O you gentle day sky!" Apostrophizing an inanimate object may involve personifying it.

From the Guide to Literary Terms by Jack Lynch.
Please send comments to Jack Lynch.
Note: This guide is still in the early stages of development.
Three question marks mean I have to write more on the subject. Bear with me.