HEIC is a file format used for storing both individual images and sequences of images. It came to prominence as the default photo storage format on Apple iPhone devices from iOS 11 onwards (replacing JPG) and macOS High Sierra. Developed by the MPEG group, HEIC files are generally 50% the size of JPEG files, but with higher visual quality. They also allow users to store metadata and image edits alongside the photo, and more than one photo in a file (useful for "Live" photos).
A .heic file is a container, indicating that the stored media is a type of High Efficiency Video Codec (HEVC) file, as defined by the High Efficiency Image File Format (HEIF) specification. Like JPG files, the HEIF specs detail that image data is stored using discrete cosine transform (DCT), which results in lossy compression. However, becuase HEIF supports a larger variety of block sizes for DCT (from 4x4 to 32x32), the resulting compression is more efficient, leading to smaller files sizes. HEIF also supports animations, thumbnails, image edits, sequences, metadata and extra image data such as alpha plane or a depth map.
Moving Picture Experts Group (MPEG)