On this Moodle site, if you add the square brackets around a word it will either take you to the pre-existing documentation page (for example if I add the brackets around Filters it will take you to the Moodle docs about filters. If the page hasn't been created, it will offer to create it for you. This isn't a standard filter but is one of the Filters used on the Moodle.org forums (see what I did there? Click there and have a read.
PS - the standard filters are indeed very useful and worth exploring.