Roughly spoken, a multi-line label which can reformat itself to shrink-wrap the contained text. See a little fortune teller for a usage example.

How does message differ from tk_messageBox? In vernacular English, tk_messageBox is aimed at a situation where a user needs to see a message, and respond to it before proceding, while message is more of a "legend" that can appropriately stay on-screen or otherwise "within reach" over an extended interval.

RS: tk_messageBox is a toplevel dialog that contains a message and one or more buttons (OK at least).