What is "inline commenting"?

In online commenting “inline comments” are comments you can add within the content of a document directly.

Comments are usually added at the bottom of a page (for example on blog posts or online forums such as here on Quora).
But if you can highlight a part of the text and add a comment that refers directly to that part, it’s an “inline comment”. Usually the inline comment is then displayed on the side of the document, or within a pop-up dialog once the user hovers over that part of the text.

Not to be confused with “inline comments” in computer programming.