A squeezebox is an accordion — the instrument with a folding bellows in the middle and buttons or keys on both ends. You pull the two ends apart and push them together, which drives air through metal reeds and makes the sound, so the name is simply a description of what the player is doing: squeezing a box. It is an informal, affectionate word. Musicians and ordinary people use it in relaxed talk; a concert programme or a music shop would print accordion. The word covers the whole family loosely, so a concertina (the small hexagonal one) also gets called a squeezebox even though it is not strictly an accordion. Because it is casual, it carries a friendly, folksy feeling — you meet it around folk music, pub bands, sea songs, and old family stories, not in formal classical writing.