The part between any two points on a circle is called an arc. An arc larger than a semicircle is called an upper arc, and an arc smaller than a semicircle is called a lower arc. A semicircle is neither an upper arc nor a lower arc.

Curly ball is the technical term of football. Refers to the kicking technique in which the ball moves forward in the air and draws an arc after kicking. Curly ball is often used by the attacker to get a direct free kick near the opponent's restricted area, and use its arc running state to avoid the human wall and score directly.