Open loops are actionable information items that have not yet undergone clarification and organization in the getting things done process. Because you haven’t decided what to do with them, they have the potential to constantly distract you per Zeigarnik effect. To prevent that from happening, you need to Close open loops.
References
Allen, D. (2015). Getting Things Done: The Art of Stress-Free Productivity (Revised edition). Penguin Books.