A toggle is a switch that has two positions, on and off. It’s a tool for switching back and forth between settings or programs, such as the way that you might toggle between two screens during video chats with friends. Toggle is also a verb that means “to change back and forth.”

The term has been adopted by software developers to describe a feature that’s activated or deactivated by a user, such as a privacy setting or the Call To Action wording on a website form. Toggles allow teams to experiment with new features in a safe environment, and then quickly bring them live for all users. Toggle is used by many leading brands, including Etsy, Facebook and eBay to deploy new features in a controlled fashion.

Savvy teams see Feature Toggles as inventory that comes with a carrying cost, and so try to keep their inventories low by being proactive about removing toggles when they’re no longer needed. Some teams have a policy of adding a toggle removal task to the team’s backlog whenever they first introduce a Release Toggle, while others put “expiration dates” on their toggles so that they will be removed automatically at some point in the future.

While the idea behind toggles is simple, their use in practice can be tricky. Because they don’t contain text on/off, users must rely on other visual cues to understand their state. It’s important to design with accessibility in mind. For example, when choosing a color for your toggles, be aware of contrast issues and potential societal or cultural implications.