A toggle (pronounced TOG) is a button-shaped switch that allows you to alternate between two positions. For example, you can toggle the light between on and off. It can also refer to a software feature that allows users to toggle system functionality ON or OFF such as an Airplane mode control on mobile devices.
In a software context toggles are typically found within options menus to enable or disable features. They should be easy to read and use, have a clear indication of their current state and allow the user to easily change the status. The labels on a toggle should be direct and descriptive of the effect of flipping it. They should also be highly contrasted against the background to make it easy for users to see whether the switch is flipped on or off. When designing a toggle, designers should also be aware of societal and cultural differences in color and labelling.
Many teams move from a model of managing feature toggles as static files into some form of centralized configuration store for easier deployment and management. When a team makes this shift it is generally wise to build out an admin UI so that product, product support and test engineers can access and modify the toggle configuration. It is also often wise to ensure that any toggles which are expected to be flipped ON in production are proactively tested with all other toggles flipped OFF so that there are no surprises when the release is rolled out.