A self inflicted group photo; When the participant of a group photo also acts as the picture taker. The number of participants in an "ussie" is not limited, but typically does not exceed 3 due to the close nature of the photo. Though not always, the background in an "Ussie" is often the focal point and subject matter of the picture...

Taking a selfie with your friend(s) or significant other.

Picture taken with not just the self, but more than one person; a group selfie.

Like a selfie, but instead of just you and or one or two other people, it's a picture of you holding the camera, and a large bunch of your friends.