What is HEIC?

What an iPhone saves photos as. It isn't really an image format so much as a container holding HEVC video frames - the same codec used for film, applied to one still. That gets a photo to about half the size of the equivalent JPG, and it's also why so little else opens one: HEVC is patent-licensed, so most browsers and a lot of desktop software can't read a HEIC at all. Big photos are usually stored cut into tiles that have to be reassembled.

What is TGA?

Targa dates to 1984 and refuses to die, because game engines and 3D packages standardised on it for textures and never had a reason to move. It keeps an alpha channel, optionally compresses runs of identical pixels, and is simple enough that every tool reads it.