When you hold a camera out to take a picture of yourself or yourself and someone else while stretching your arm out long. It avoids the peskiness of having to ask some stranger to take your picture. You just hold your arm out and turn the camera towards you and ta-da great picture for your facebook page!
Nobody was around to take my picture in front of that amazing lake so I just did a longarm and got a great shot of me and the lake!
A player of the game Counter-Strike who posseses high skills on customed knife maps (ka_)
"Hey Noobboy, you are a longarm ! "