Guide access is an Accessibility feature that lets you lock the iPhone or iPad to a single app. For as long as guided access is enabled, only that one specific app can be used, and there's no way to exit it for the Home screen or any other app. Guided Access can be extremely useful in education settings, to help kids focus for learning math, language, and other skills, and for working with people on the autistic spectrum. Whether it's a writing app, drawing app, music app, math app, or a story, video, or reading app, guided access helps make sure that all attention remains on that app.
Note: Guided access can also be used by kiosks, restaurants, store, and other businesses to create a dedicated information or transaction device, and it can even be used to create a "guest mode" so you can hand your device to someone and let them use Safari, iBooks, Video, or a game without having to worry about them snooping through your personal information.