I have always called it Pig Weed. Easy to pull but don't let it go to seed.

Here is a link that might be useful: More info

That one's better than the one we get in our yard--I call it dead skunk weed! It has little berry-like things on it that look like tiny green tomatoes and when you pull it it smells like a smelly animal that died and has laid in the sun for several days! And the smell stays on hands through several washings, yuck.....