Basketball is a sport played by two teams of five players on a rectangular court. The objective is to shoot a ball through a hoop 18 inches (46 cm) in diameter and 10 feet (3.048 m) high mounted to a backboard at each end.
It is one of the world's most popular and widely viewed sports. The National Basketball Association (NBA) is the most popular and widely considered to be the highest level of professional basketball in the world.
The only essential equipment in a basketball game is the ball and the court: a flat, rectangular surface with baskets at opposite ends. Competitive levels require the use of more equipment such as clocks, score sheets, scoreboard(s), alternating possession arrows, and whistle–operated stop–clock systems.
Variations of basketball are activities based on the game of basketball, using common basketball skills and equipment (primarily the ball and basket). Some variations are only superficial rules changes while others are distinct games with varying degrees of basketball influences. Other variations include children's games, contests or activities meant to help players reinforce skills.
There are principal basketball sports with variations on basketball including Wheelchair basketball, Water basketball, Beach basketball, Slamball, Streetball and Unicycle basketball.