The Green Heron (Butorides virescens) is a small member of the heron family. It has much shorter legs than some of the other waterfowl you will see in Maryland, like egrets and the Great Blue Heron.
The Green Heron is so named, due to the dark green coloration of its crown feathers.
Their range is listed across the state of Maryland, but in my experience, they are much rarer than the Great Blue Heron. The only place I have seen a Green Heron in two years is Assateague Island.