What do you mean by synchronous reactance?

Synchronous reactance X s= (Xl + Xa)

The value of leakage reactance Xl is constant for a machine based on its construction. Xa depends on saturating condition of the machine. It is the
addition of Xa , which represent the armature reaction effect between two synchronously acting magnetic fields that makes the total reactance Xa to be called syncheornous reactance.