Here is a common question at this time of year. It comes from the answer line at ISU.
The question is, "I have a patch of grass in my lawn that turned brown early last fall and is not greening up this spring. What is it?"
It is Zoysiagrass, a warm-season species that is becoming an increasing problem in Iowa lawns. It is very hard to kill. Roundup will set it back, but it always seems to survive, even after multiple applications. I have seen people treat it with Roundup, then remove the sod and sod Kentucky bluegrass over the spot. It still comes back.
Good luck if you have this one in your lawn and want to get rid of it.