A toggle is a switch that has two positions, on and off. It is used to control things that change over time, like changing the case of selected text on a keyboard or alternating between screens while video chatting with two people at once. Toggles are often used to perform A/B testing by sending users down different codepaths based upon their cohort status and tracking the impact of each path on user behavior.
Many teams use static files for managing their toggle configuration but this quickly becomes cumbersome when a project reaches a certain scale. This is why many of the best practice Feature Flag approaches recommend moving to some type of centralized toggle configuration management system, usually built on top of existing application DB. In addition to making the management of toggle configuration easier this approach also makes it much easier to test your system with all feature flags flipped on.
It is important to use clear and consistent labeling on your toggle switches so that users have a good understanding of what will happen when they click the switch. This includes the choice of a color for your toggle states and an evaluation of both contrast and cultural implications (for example, using red as an on state may be counterintuitive to users in some cultures). When designing your toggle switches, remember that they are essentially a visual control for a process so ensure they have the same movement and color cues as other controls on your site or app.