Angular velocity in degrees per second.
A Rigidbody2D can only rotate around one axis (the Z axis) so the angular velocity is a single float value rather than a vector. Typically, the value of this property is not set directly but rather by applying torque to the rigidbody. The angular velocity will also decrease automatically under the effect of angularDamping.
Additional resources: linearVelocity, AddTorque, AddForceAtPosition & angularDamping.