Power play is when only two fielders are allowed to field outside the "circle". If you see the ground, there is a dotted circle marked on the ground around the wicket.
The idea is more fielders in an "attacking" position trying to take wickets while making scoring opportunities easier for the batmen who take the risks necessary to score runs.
There are 15-overs of power play in a 50-over match - One 10-over stretch at the start of play and the other 5-over stretch can be taken at anytime at the fielding captain's discretion.
Thanks Abby. That explains the power play. I guess it's advantageous to the fielding side. Power play could be somewhat new as I was not familiar with it in cricket.
And it's advantageous to the batting side too in the sense that if they can hit past (or over) the close-in fielders it's easy four runs because there are only two players outside the circle.