This term is typically seen in Italian (sempre) and is used to modify a musical directive. Take for example, the term "sempre staccato". Sempre (or always) would modify the term staccato (meaning detached or separated). The intended result would be that the indicated passage (or entire composition) be performed in a staccato manner.
See also [Eng.] always; [Fr.] toujours; [Ger.] immer; [It.] sempre.