What is this grass?
This is yellow nutsedge. It is a weed and will spread. It is hard to control, since it grows from tiny bulblets which often stay in the ground when pulled. Don't let it make seed. Here is a page about it: http://extension.umd.edu/hgic/yellow-nutsedge
A product called Sedgehammer is effective as a last resort.
Thanks! I will try to get rid of it. I appreciate the help.