The Sound Hole or holes are the circle cut out of the guitars front where the amplified vibrations echo from.
Sound holes are usually just below the fretboard of a guitar, although many companies offer guitars with sound holes in other places.
some Ovation Guitars do not have a sound hole below the fretboard, instead they are placed to the right or left ot the last frets.
sound holes are commonly round in acoustic guitars, although they do not have to be.
hollow body and semi-hollow body guitars commonly have the "f" shaped sound hole. Rickenbacker semi and full hollow body guitars use a shark fin-like cut. Electric guitars do not rely on a sound hole to amplify the string vibration, instead the sound hole effects tones and other sound related features as well as style, size and weight.