IMHO, a ski in/ski out TS is one which you don't have to drive or shuttle from the TS to the ski lifts.
As examples:
Many of the Whistler BC TS are Ski in / Ski out.
The Marriott TSs in Park City and Tahoe are both next to the lifts.
Here is a link to a similar question
Bill -
Yes, I mean you don't take a shuttle or drive to the lifts.
The link - doesn't 'link' anywhere, could you try it again.... thanks