A cadence (from the Latin cadere, “to fall”) is a succession of notes and chords that signals the end of a musical phrase. Cadences are analogous to punctuation in language: just as different punctuation symbols denote varying degrees of completeness (consider the comma vs. the period), different cadence formulae provide various important musical cues about the overall structure of a phrase.
Cadences are usually easy to identify by ear because they are formulaic and they come at the end of musically intelligible units. Indeed, the definition of cadence is closely (and circularly) bound up with the conventional definition of phrase: in general, you know you’ve heard a cadence because you’ve come to the end of a phrase, and you know the phrase has come to an end because you heard a cadence. These musical punctuations are effected by the arrival– and typically a pause – upon certain key pitches and harmonies that our ear hears as the “home” of a song, or section thereof. This “home” is also known as the song’s “key”.. Here is the cadence ending “God Bless America” – notice its “falling” sound as it comes to rest on the final “home” note of F, which is the “key” of the song.