Angular velocity in degrees per second.
Unlike a 3D Rigidbody, a Rigidbody2D can only rotate around one axis (perpendicular to the plane) so the angular velocity is just a float value rather than a vector. Typically, the value of this property is not set directly but rather by applying torques to the rigidbody. The angular velocity will also decrease automatically under the effect of angular drag.
Additional resources: velocity, AddTorque, AddForceAtPosition, angularDrag.