Can you explain what is the phrase "Separation from service" refers too, on form 5329

In March 2015, at the age of 57, I was laid off.  In July 2015, I withdrew a portion of my previous employer's 401K plan.  On December 28, 2015 I started a Job in a city more than 75 miles from my previous job and home. I was required to relocate as a condition to accepting the position.  The cost of living is substantially higher and the proceeds from the sale of my home will not allow me to have a sufficient down payment for a home in our new location.  If I withdraw additional funds now (July 2016), from the same 401k planand use it as part of the down payment on a home in the new city. Will I be required to pay the 10% early withdrawal penalty in 2015 or 2016?