When the angle of attack on an aerofoil is measured relative to the zero-lift axis it is true to say the lift coefficient is zero when the angle of attack is zero. For this reason, on a cambered aerofoil the zero-lift line is better than the chord line when describing the angle of attack.

What does zero mean in a lift?

: the angle of attack of an airfoil when the lift is zero. See the full definition.

What is the zero lift angle?

The angle of attack at which an airfoil does not produce any lift. ... Its value is generally less than zero unless the airfoil is symmetrical.