Org is a difficult subject. Talking about any one aspect of Org Mode is like discussing the peak of an mountain. The roots of Org Mode go very deep.
Often people will discuss folding and the ability to tab cycle a headings tree. Or, it is often compared to Markdown. Org IS a markup and document interchange format like Markdown, but it is also so much more.
Fundamentally org mode is 2 very different things and fairly hard to describe:
- Org Files - A text based document markup language similar to markdown.
- Org Mode - A wide variety of tools for operating on and working with collections of these files.
- Org Extensions - I know I said 2 but Org has a wide variety of tools built around the mode and api’s extending it in many creative ways. Although not org mode itself most people refer to these tools when they think of Org Mode.