This is the definition of flag on Dictionary.com:
5.to mark (a page in a book, file card, etc.) for attention, as by attaching protruding tabs.
I have an idea of what a tab is, but what exactly does it look like?
One common kind of protruding tab…
When I had an accountant filling in my tax returns (which ran to many pages), he used to attach tabs like that on certain pages – red where I needed to sign something, and green for sections I was supposed to read and double-check (which I rarely did! 🙂
Source : Link , Question Author : Theo , Answer Author : FumbleFingers