Q:

Temperature of empty space

Is the temperature of empty space defined?  What is it? 
I am not talking about the cosmos.  I mean really empty space, without particles. 

A:

If there are no particles or radiation there cannot be a temperature defined as it is dependent on the average kinetic energy . 
 . 
Now in the real universe there are no completerly empty spaces from particles or radiation.  The cosmic microwave background radiation has a black body distribution temperature of 3K .