An org mode syntax I use heavily that I rarely see mentioned, including in this cheat sheet, is the obscurely named Radio Targets. Enclose any term or phrase in <<<tripple angle brackets>>>, hit C-c C-c on it, and then any previous or further instance of it in the same buffer will be automatically linked to it from then on. Incredibly useful when you're wroting notes on a long book for example and want to keep track of the instance when a term was defined. Turns an org file into its own wiki.
https://orgmode.org/manual/Radio-Targets.html