Hi there, and welcome. It's near impossible to tell from the distance and resolution of these photos. Try getting up close (in-focus) photos of the grass blades itself, Here's a good site that describes the features you're trying to capture. Wiping the yuck off the lens of your cell phone camera is advised too, you're trying to capture some fine details.
http://plantscience.psu.edu/research/centers/turf/extension/factsheets/cool-season-turfgrasses-id
Guessing like most, you have a blend of different kinds of grasses in your lawn. (We typically call this a Norther Mix, or NoMix) You may be looking at an area that was patch seeded with a differing kind of grass than the rest.
What is a weed is largely subjective. Take a look at the stickied post at the top of the forum, and let us know what level of lawn you're looking to have, and willing to put in the effort for(Tier 1, Tier 2, Tier 3) and try and get some closer photos of the distinctive attributes of that plant you're looking to identify, and I think we could offer you much better advice.