The Grand Slam is a tennis tournament, while the ATP is an orginization. (Association of Tennis Professionals.)
The tennis Grand Slam is a annual tournament. There three tournaments within the Grand Slam. The US Open, the Wimbledon, and the Australian Open.
Wimbledon Grand Slam Tournament is played on Grass Court.
The US Open is the ony Grand Slam tournament that does not use tie breakers in the final set.
The Australian Open