For an overview on creating, visualizing, and simulating mover constraints, including AngularVelocity, see Mover Constraints. Also see Roblox Units to understand how Roblox units compare to metric units.
An AngularVelocity constraint applies torque on an assembly to maintain a constant angular velocity.
The AngularVelocity constraint applies torque that attempts to maintain a constant angular velocity. If you want to control the amount of torque applied, use a Torque constraint. Alternatively, if you only need initial angular velocity, set the AssemblyAngularVelocity method directly on the assembly.
Relativity
Application of velocity can be controlled through the constraint's RelativeTo property. If set to World, the angular velocity vector is used as is. If set to Attachment1 and the constraint's Attachment1 property is set to another attachment, the angular velocity will be affected by that of the other attachment as seen by how the upper-left red part's velocity affects the attached blue part's velocity.
Setting RelativeTo to Attachment1 also exposes the ReactionTorqueEnabled property.