HDR gets used loosely — as a marketing word, a camera mode, a vibe. This guide is the plain version: what the term actually claims technically, how HDR content is really represented in a file, and how to tell whether an image genuinely has HDR data or just looks punchy.
Each article below is short and stands on its own. If you just want the one-paragraph answer, start with What is HDR, actually? — everything else builds on it.