Inline note
From MTG Wiki
Inline notes allow various users to communicate about specific parts of an article. For a similar function in layouts, use a sticky note.
All notes should be resolved and deleted before a story is published.
Notes in Content Station
To create a note in Content Station, place the cursor where the note should be and click the Note button in the Multi-Channel Text Editor. This will place a new note. An hourglass-shaped icon will indicate that there is a note in the text; double-click that icon to read, reply to, or delete the note (once the issue has been resolved).
Notes in InDesign
InDesign's Notes panel is available under Window—>Editorial.