The term 'apartment piano' refers to two types of pianos that are designed to fit into small spaces. An UPRIGHT piano is a type of piano that stands vertically and has a smaller footprint than a grand piano. It typically has seven letters. A SPINET piano is a type of UPRIGHT piano that is even smaller and has a shorter keyboard. It typically has six letters. Both UPRIGHT and SPINET pianos are ideal for small spaces, such as apartments, and are often used by beginners or those who don't have the space for a larger piano.