Have only heard them called "tennis sets" when they were made of "bone china". If you look at "typical" tennis sets they were smaller plates - for petite eating.
I have inherited 2 full sets and some are still in original boxes - they were called snack sets or luncheon sets. From the 20's to the 60's when playing cards, women having luncheons, home weddings, canasta, etc were regular social event. You will find them clear glass, milk glass, ironstone, and china.
You can find the glass ones everywhere here (garage sales, GoodWill, second hand stores, estate sales, etc). Like Mart said, they don't demand a high price. (ironstone overall weren't that popular due to weight - so if yours are more modern they are more lightweight.)
In my area/California/Florida/Louisiana/Arkansas/Mississippi you would be doing really good if you get $8 - $10 for these.