A Half cadence is a partial resolution, mostly used in classical music.

IV -> V7
F -> G7

Usually, they are used in the following eight measure pattern:
1 2 3 Half 5 6 7 Full

You can think of half cadences like commas (,) and full cadences like periods (.). Half cadences exist because of the assertion in classical western music that cadences cannot cross between bar lines.

However, you can also think of it as just being a full cadence since it ends on a full cadence.