Tenuto is an articulation direction (literally, 'to hold') used in musical notation which can have several different meanings. By far, the most common usages of the tenuto are (1) to hold a note for its full value or, more usually, slightly beyond (i.e., in a sustained manner), and (2) to give a note mild dynamic emphasis. Sometimes both of these are intended at once. The context of the tenuto is a guide to the intended meaning.
As a dynamic instruction, tenuto implies mild dynamic emphasis. Heavier dynamic accentuation would be indicated with an actual accent mark, heavy accent mark (marcato), or sforzando and indicates an effect that is more percussive in nature. The dynamic suggested by tenuto is more along the lines of making the note ring out.
The meaning of the tenuto marking can modified when it appears together with other articulations. In conjunction with a staccato dot, it is equivalent to staccato dots under a slur, i.e., non-legato or detached. When it accompanies an accent mark, because the accent indicates dynamics, the tenuto unambiguously takes on its meaning of full or extra duration. A series of tenuto marks, one after another, is an indication to play the notes slightly detached and with a slight accent.
Compare with portato.