These two words have connotations but they can be used to define the same thing. A selfie would be for most people a photo taken with the smartphone/camera in your hand or on a stick, while a self portrait would be a photo with a dedicated camera on a tripod.

Also the “obvious skill difference” that you talk about comes from the photographer, not from the way they call their shooting style ;)

I’m not quite sure I’m ready to call a 4x5 view camera selfie, well, not a selfie.

It’s just a vastly cooler one.

I’d say a selfie is when the person in the image is obviously holding the camera.

In a self portrait you are not holding the camera, the camera is on a tripod or something similar and it could have been taken by someone else.

That is how I differentiate between the two.

A self-portrait is a self-representation in art, typically created by an artist using various artistic mediums, such as painting, drawing, or photography. It often involves careful composition and can be highly expressive and artistic. It has more care put into it.

A selfie, on the other hand, is a casual self-portrait taken with a smartphone or camera, typically using the front-facing camera. Selfies are often quick, informal snapshots and are commonly shared on social media. While selfies can be artistic, they are generally associated with more everyday and spontaneous self-representation.