What is the Biblical definition of "prophecy"?

In common parlance, prophecy is often considered to be "predicting the future." For some, it conjures up images of telephone psychics and the like. Others might envision a crystal ball. It generally has a mystical connotation of some type. On the other hand, the "prophets" of Scripture (e.g. Malachi, Habakkuk, Jonah) seem to be doing something different. Making explicit predictions about the future seems to be a small part of their function as a "prophet." So my question is: **Biblically speaking, what exactly is prophecy?** Is there a Biblical definition that matches the actual practices of the prophets? ------ *If possible, please support your answers using the 66 books of Scripture that are found in the Protestant Bible.*