There is no objective way to define "weeds." A weed is just a plant growing where it is unwanted.
Learn to love your dandelions and crabgrass, welcome them into your lawn. Mow and landscape to showcase their presence along with your grass and other ground cover.
When you have done this, no plant in your lawn will be out of place or unwanted. You will have no weeds.
Or, you could poison the crap out of them.