If you do not want iOS to save images in the HEIF format, open your "Settings" app, and select Camera → Formats → Most Compatible. Selecting Most Compatible means that iOS will now save images in the JPEG format.
HEIC is the new file type for photos in iOS 11. That's for iPhones and iPads with an A9 processor or newer, so iPhone 6S, 6S Plus, iPad Pro models and the recent 2017 iPad 9.7.
HEIC is another name for HEIF, which is short forHigh Efficiency Image Format. It’s the still image version of HEVC, which is the latest video codec.