what is a file with .heic extension?

The HEIF format (.heic for image files and HEVC codec for videos) have been used by Apple on the mobile devices for a few years. It is enabled on an iPhone or iPad if you set the Camera format to "High efficiency". This format has a better compression compared to a JPEG, resulting in a smaller file size for the same image quality.

See Apple's description for more details: Using HEIF or HEVC media on Apple devices - Apple Support

It is a newish file format with better image compression than JPEG. As Barney-15E says, it is the current default with iPhones.

Current Macs have no problem with it.

Do you have a particular issue?

It's an image from an iPhone--well, not necessarily, but mostly. You can make them with other things, but the iPhone camera app defaults to heic.