Visual testing is like snapshot testing with images. So when your application is in the state that you want it to be in, you verify this as a human being, and then utilize tools to take a picture of your application in that state.
Visual testing isn't a new concept, but the technology was previously flaky. But now, Applitools is using AI and machine learning to be able only to detect the things that we care about as human beings.
Visual testing catches issues that your scripts won't detect, and Applitools is especially powerful at it. The processing gets offloaded onto the Applitools servers, and snapshots of your app are tested on multiple platforms so you can be confident that no visual bugs get created anywhere!