Headwind or Tailwind?

Another question I find interesting is: if you were flying to South Lake Tahoe at 13,500 ft MSL (since you want to be well clear of the mountains ... plus you want to brag to your friends that you flew that high...) and you see that your ground speed is 135 KTs/hour but your Air Speed indicator reads 125 KTs... do you have a headwind or a tailwind?