If your understanding of cricket is limited, it is sufficient to know that a googly is a kind of secret weapon used by very skilled players.

Cricket involves a series of individual mini-contests between a bowler from one team and a batsman from the other. Bowling is an art and individual bowlers develop specialist skills to defeat batsmen in these one-on-one encounters.

One such specialist skill is the technique of "spin bowling": under certain conditions you can bowl the cricket ball with rapid rotation so that when it bounces on the pitch it will deviate from its normal straight path, making it difficult for the batsman to hit the ball cleanly. Typically, for a given bowler, these deviations will be in one direction only, depending on whether the bowler is left-handed or right-handed and his style of delivery. So the batsman can get used to these sneaky bounces and instinctively compensate for the spin, raising the chance of hitting the ball. After a while the batsman can anticipate where the high-speed ball is going to go as it bounces.

Now for the secret weapon. With no change in delivery style (the run-up, the arm movements), but just a tiny adjustment in wrist action, a skilled spin-bowler can make the ball bounce the "wrong" way; the batsman gets no warning that this one is going to be different. The googly is a surprise missile that gets through the countermeasures. For enthusiasts it can be a joy to watch the bewilderment on the defeated batsman's face...

More Info: en.wikipedia.org