Power in AC circuits
Here's a picture I did for another answer - it shows how the power waveform looks for varying degrees of power factor: -



Top left is PF=1 i.e. a pure resistor - the power waveform never goes negative. Top right is for a complex impedance where the current lags by 60 degrees (a resistor in parallel with an inductor would achieve this). Bottom left is purely for an inductor and, as you should be able to see, the power waveform has an average value of zero.


  what would negative power in negative cycle represent?


That represents power being delivered back to the supply.