The rectangular area in front of the basket that is bounded by the baseline, the foul lanes and the free throw line. In the NBA and FIBA leagues, the key is 16 feet wide, while in the NCAA, the key is 12 feet wide.
Offensive players are prohibited from remaining inside the key for more than three consecutive seconds, a violation that results in a loss of possession. In the NBA, defensive players are also prohibited from remaining inside the key for more than three consecutive seconds if they aren't actively guarding a player. The team committing this violation is charged with a technical foul. The key is also known as the "free throw lane".
This area is named the "key" because, originally, the rectangular area was narrower than the diameter of the free throw circle. With the free throw circle as the head and the painted rectangular area as the body, it formed the shape of a key. The key was widened for the 1951-52 season because certain players scored at will since they could position themselves closer to the rim with minor limitations.
FIBA basketball used a trapezoid-shaped key before switching to a rectangular one in 2010.