Beach volleyball is a team sport. There are two teams of two players each on a sand court divided by a net. The object of the game is to throw the ball over the net so that it lands in the opponent’s court, and the other team cannot return it. It is an Olympic sport.
Due to its origins as, literally, a game played on the beach, the outfits worn are traditionally similar to swimwear. For women, the outfits worn even at the Olympics and other high level games are little more than bikinis, consisting of a tight crop top and tight bikini bottoms. In some cases, they are actual bikinis.
At the 2004 Athens Olympics, men had to wear tank tops as well as shorts. Also, tank tops had to fit close to the body, with open arms and shorts could not be baggy or reach the knee. 
An important part of beach volleyball is the hand signals that the player nearer the net makes to his or her partner (the server) just before the serve advising on intended strategy. To stop their opponents seeing the signals, they are made behind the player's back. This gives an excuse for people to publish photos of close-ups of these signals that "coincidentally" show the player's bottom.