Based on the shape of the leaves, It looks like something in the Brassicaceae Family, more specifically probably the Genus Brassica. Although that is far from certain without knowing your location and also maybe not without seeing it bearing flowers.
The characteristic that identifies this as a Brassica to me is the lobes occurring on the leaf stem below the main leaf, although there are other plants that do this too.
This family includes Mustards, Radishes, Cabbage & many other food crops however, there are many, many wild & introduced variants that are considered weeds, even at that though, you would need to more precisely identify it based on location and mature specimens to determine if it is useful or not.
You can tell it's a weed if you didn't plant it and if you don't want it (whether it's a nice plant or not).
It looks a lot like arugula to me, but it looks rougher. It's possibly edible, and is very likely related to arugula, but I wouldn't risk eating it without certain knowledge of exactly what it is. Hopefully you'll get an ID on it.