A plant is only a weed if you do not want it in that location. Sounds like you don't, so it's a weed.

It can be killed with Weed-b-Gon or Weed-b-Gon Chickweed, Clover, and Oxalis Killer. Read the directions for tips on when you can reseed after spraying.

Reseeding depends on where you are. Give us that info and we can help with reseeding advice. If you are in Silver Spring, MD, it's too late to reseed most grasses. You might get 50% germination if you go with a very fast germinating grass like rye.

It looks like Duchesnea or Potentilla indica. Tbh, unless this in a trim and tidy front garden I’d just accept it as my lawn. This species thrives in the kind of shady, poor soil conditions which are not very conducive to grass.

Thank you, friends. Both answers were helpful. And, yes, I'm in Silver Spring, MD. So I will wait for the spring to reseed. Any ideas of what I can do to enrich the soil meanwhile?

I'm not going to advocate seeding this late in the fall nor spring seeding. I'll let the northern tier folks help you out with that. As for enriching the soil, if you have access to a ton of mulch, an inch or so of mulch works wonders. Or you could apply an organic fertilizer like soybean meal, alfalfa pellets, or, as I just found on a different post, Dumor poultry crumbles. Apply these organics at 15 pounds per 1,000 square feet now and again about 3 weeks prior to your last frost date in the spring. Organic fertilizers are good for the soil, because they feed the beneficial microbes living in the soil. It is the health of the soil microbes that determines how good your soil is. And I guess soil chemistry has something to do with that, but the best chemistry is no good without healthy microbes.

Thank you. I will focus on just that, doing what I can to prepare the ground for next year.