What is the name of this plant?
This is an old-fashioned groundcover known as cypress spurge. It's Euphorbia cyparissias. If you break a stem, you'll find a milky sap, typical of euphorbias.
Here's more about it as a landscape groundcover plant: https://www.illinoiswildflowers.info/weeds/plants/cypress_spurge.htm
It is not native and can become a nuisance in the landscape. It has also been listed as a non-native invasive plant in the mid-Atlantic region, of medium to low invasiveness.
If you grow it, be sure to keep it out of natural or wild areas, especially when parkland is around. It can be very difficult to get rid of once it gets into an area.
Thanks for a great answer, and thanks for mentioning that it was not native! I wanted to include that as part of my original question but forgot. I saw these on the campus at St. Johns College in Annapolis, and it surprises me that they are using invasive plants. (but they are so FLUFFY!) I will not be planting any of these.