When singing or playing from a piece of sheet music, you’ll sometimes encounter the word tenuto over a note, telling you to make sure you hold it for its full value. Sometimes it applies to a rest instead of a note.
As long as the rhythm is kept, it's usually okay to end a note or a rest a tiny bit early — for example, in order to reach a more difficult note. But when you're instructed to perform it tenuto, it’s important not to cut off the note or rest too soon, but to hold it so the listener notices its full effect. Tenuto is Italian for "held" or "sustained." Often, just the symbol is used, a small straight line above or below the note or rest.