Looks like henbit (Lamium amplexicaule). Yes, a weed.

Henbit, "Lamium amplexicaule", a memer of the mint family of plants that grows best in thin turf area with a moist, nutrient rich soil that is shadier, a winter annual. The simplest means of control is to get the turf thick so the turf crowds this out. Since it is an annual what was growing last year will not be groing this next yeat, although seeds have already germinated and are ready to grow in areas the plant finds nice and comfortable places to grow.
I have this growing, if I allowed it, in some pea gravel that has been in place for a number of years where dust from the air and other sources of organic matter have filled in the spaces between the wee stones. Where it is found I pull the plants before they set seed, but evidently the birds really like those seeds and drop them all over the yard because I see it frequently.