Projectiles are objects that are under the sole influence of gravity. They represent a form of two dimensional or projectile motion. Neglecting air resistance, a projectile has a constant horizontal velocity and constant downward free-fall acceleration. In the absence of air resistance, projectiles follow a parabolic path or trajectory.
In order to produce motion that is not strictly linear, an object (projectile) must have 2 independent motions that act at right angles to each other.
With curved motion, now all kinds of motion are possible.