If just the occasional strand is like this, it's probably just a piece of hair that was snapped, leaving the end a little thinner than the top. If all of them are like that, I would say maybe it's from your health improving. Looks like a nutritional difference causing your hair to come in thicker. Are you taking any vitamins, eating better or have you recovered from any illness in the last year or two?
edit: It might also be that a hair has shedded and then another one grew back in. I think new hairs that grow in taper off at the ends like that naturally. A blunt thick end usually only appears on hairs that have been cut. A lot of my hairs do this too. I think it's normal.