Straps

From GuitarWiki

Guitar straps allow for the guitar to be held in a comfortable and convenient position. The long piece of material is strapped from on end of the guitar body to the other, usually from where the neck meets the body to a position behind the bridge via pegs where the strap will attach on. Occasionally, a guitar will only have one of these "pegs" on the back of the guitar. In this case, the strap will attach by a string tied just above the neck, under the strings, near the tuners. So with this, the guitarist puts the strap over their left shoulder (assuming they are right handed, fretting with their left hand), and thus can stand and walk with the guitar whilst playing, without the worry of holding the body themselves.