The deceptive cadence is a weak cadence, and can be considered in many ways the opposite of the half cadence - where the latter involves a 'resolution' to a V chord, the deceptive cadence is a resolution from the V chord to any non-I chord, most typically some variant of ii, IV, or vi. This progression serves to create a hanging, incomplete feeling.
- In English: you know that happy, satisfied feeling you get when a song ends and all seems right with the world? Yeah, this doesn't give you that. Usually it will go on to resolve properly.