Apple has finally enabled support for multiple cameras in iOS 13 and iPadOS, a feature that has been available in some form or another on a number of Android devices over the years. This feature is also supported on the Mac for a while.
Multi-camera support will only be available on new devices such as the iPhone XS, XS Max, XR and the newest iPad Pro (via iPadOS).
There are also certain combinations that you can perform on these devices. You can use both a regular camera and a telephoto lens on the back of the iPhone, as well as a regular rearview camera and a selfie camera. There are even combinations that allow you to use the TrueDepth Selfie Camera.
And when Apple introduces its three-camera iPhones later this year, they will support multiple camera combinations for their ultra-wide-angle cameras.
Multi-cam supports capturing photos, video, and audio from multiple cameras simultaneously. Here is a detailed description of which video resolutions and high-resolution photos will be available, which frames per second and whether they will be grouped (oversampled) or not.
Apple will release the multi-camera API as part of iOS 13 for developers to add functionality to their applications or create new ones, especially for capturing multiple cameras.