1) Projectile motion describes the trajectory of objects thrown or projected into the air. It is the motion of projectiles that are subject only to gravity.
2) Projectiles have two velocity components - a horizontal component that remains constant, and a vertical component that changes due to gravity. This results in a parabolic trajectory.
3) There are two types of projectile motion - horizontally launched, where the initial vertical velocity is zero, and vertically launched, where the velocity has horizontal and vertical components.