An upright piano is a piano in which the soundboard and plane of the strings are vertical and perpendicular to the keyboard, in contrast to the horizontal structure of grand pianos. Their smaller size means that they have shorter strings and shorter soundboards, which results in a subtle difference in timbre and a smaller dynamic range as compared with grand pianos. Further contributing to the reduced sound volume is the fact that they emit sound from the back end, which is usually placed against a wall, instead of from above.
Another major difference is the mechanism that causes the hammers to strike the strings when a key is pressed, which results in a different feeling in the player's fingers. In upright pianos the vertical orientation of the strings necessitates the use of springs to return the hammers to their at-rest position, whereas in grand pianos the hammers return to their at-rest position under their own weight due to the force of gravity. In addition, grand pianos utilize a double escapement mechanism that allows keys to be played in rapid succession, without first letting them return all the way to their starting positions. The result is key repetition (i.e., when a player repeats notes quickly, such as when playing trills) is much smoother and faster than with upright pianos.
The main advantages of upright pianos as compared with grand pianos are their taking up much less floor space, their lighter weight, and their substantially lower prices. This makes them better suited for use in homes, schools and small entertainment establishments.