Rotation: around y-axis.
Symbol: theta q

Main rotor collective pitch increases main rotor force.
This gives helicopter possibility to perform ascend/descend (vertical motion).

Cyclic pitch or "longitudinal cyclic", directs main rotor force along x-axis.
This induces longitudinal motion by inclining main rotor force in x-direction.

Tail rotor collective pitch or "tail" acts on tail rotor force to turn helicopter around its main rotor axis.

Related links:
~ >Yaw (z)
~ >Roll (x)
~ >6DOF