Mixture of truth and falsehood; neither true nor untrue, but something in between. The world is not untrue (a-sat) but mithya. (Glossary for the Vahinis)

You have to churn the milk if you wish to separate and identify the butter that is immanent in it. So too, you have to carry on certain processes of thought and action in order to get the hard core of faith that this world is a funny mixture of Satyam and Asatyam, that it is Mithya, in fact. (SSS Vol.1, p. 29)