In the settings of a web application, admins can select "custom fields" of different types: number, selector, multi-select, etc.
We added an option that allow user (not admin) to type their own option, just like an "other" option where user are free to input what they want.
We currently added an option for admin to allow free editing named (translation): "Allow create option on the fly".
Still it's not clear: we could think that it actually creates the option on the fly, making it globally available. In fact, it just allow to add a free text, just like when we have "other" in a form