Tempo refers to the speed of a musical piece, while key refers to the tonal center of a piece of music. While there is no direct correlation between tempo and key, they can influence each other. For example, a piece in a major key may sound brighter and more energetic at a faster tempo, while a piece in a minor key may sound darker and more somber at the slower tempo. Additionally, some keys may be more conducive to certain tempos than others. For example, the key of C major is often associated with fast, upbeat tempos, while the key of E minor is often associated with slower, more somber tempos.