TKTK is a writing convention used by authors to mark a place where additional content will be added at a later date.

It likely originated from "to come", was shorted to TK to make it more unique, and then lengthened to TKTK to create a visually arresting and easy to spot marker.

We use this convention in the Lionsberg Wiki, which enables easy searching and immediate linking to all incomplete sections since TKTK does not appear in any actual words.