If you do not want it growing where it is growing then it is a "weed", but if you don't mind and can allow it to grow it could be a flowering plant.

The third picture makes me think mugwort but not the first two pictures. Can't say for sure.

It is a wild geranium, probably Geranium dissectum, native to the US.

Torajima-Thanks for helping me put a name to one I have pop up around. I knew it was a Geranium, but it wasn't in my Peterson's--too many Geraniums to get them all in there, I suppose. However, it's not native to the US, just widely naturalized.