“Tempo” is an Italian word meaning time, and in music terminology simply refers to the speed at which a work is played and heard. In notated music (Classical music in particular) the author usually indicates the speed at which he would like to hear the work played, typically using Italian words like Presto (very swiftly) and Lento (very slowly). In most popular songs, however, the intended speed at which they should be performed can be inferred from their lyrics, along with other musical attributes like genre (disco, hip-hop, rock ballade, etc.) and rhythmic elements.
Even gussied up with the term “Tempo” the intended speed of a musical work is not an independently copyrightable element of a song, like its melody, lyrics, and accompaniment. This is because the speed at which a work is performed, whether indicated by the author or not, is a basic component of musical works, like pitches and rhythms. While pitches, rhythms, and words can be combined to create original copyrightable material that expresses the ideas of a particular author, performance speeds cannot be similarly combined to rise to a level of original copyrightable expression.
Under the heading Rhythm there is an explanation with audio illustrations, of the difference in meaning of the terms “Tempo” and “Rhythm”.