Program music is instrumental music that has some extra-musical meaning, such as with regard to a historic event, a scenic description, a human drama or a literary idea. It contrasts with absolute music, in which there is no intentional reference to anything other than the music itself.
Rather than being a rigid category, program music should be considered a matter of degree. For example, with two works both having a title related to some natural phenomenon, such as the chirping of birds or a rushing stream, or to some human emotion, such as love or jealousy, one might clearly remind listeners of that phenomenon or emotion while the other might remind them of it only vaguely, if at all.