A half cadence in music is a melodic and harmonic cadence that ends the section of music in such a way that it ends on the V. The V is always major; otherwise, it is considered a deceptive cadence. Keep in mind the V is major even if the song is in the minor key or some freaky mode.
The next strongest cadence after an authentic cadence and plagal cadence. It is, however, stronger than any deceptive cadence. It is commonly used to end a section of music, but almost never to end a song, except for effect.
It is also the last chord in a flamenco progression and a I - IV - V progression.