This is a weed called yellow nutsedge. It looks like a grass, but it is not, it is a perennial sedge.
Here is our page on it: http://extension.umd.edu/hgic/yellow-nutsedge
Try not to let it go to seed.
The page above discusses control methods. Often the selective herbicide Sedghammer is used.
Given the amount you have, you might think of killing the whole area back with a non-selective (kills all green stuff) containing glyphosate, and then re-seeding this fall.
Now is the time.
Here is our lawn page: http://extension.umd.edu/hgic/plants/lawns