Complex sentence: A jam block is a percussion instrument which is a modern, hard plastic version of the more fragile wood block, and is sometimes referred to as a "clave block", "gock block" or "tempo block".
Split into simpler sentences: A jam block is a percussion instrument which is a modern, hard plastic version of the more fragile wood block. It is sometimes referred to as a "clave block", "gock block", or "tempo block".