Why do ants stop everytime they meet?

Most common ants rely almost entirely upon odor trails. This is how ants form an odor trail to and from food supplies. When a worker ant finds a lot of good food, she gets quite excited. A faint scent comes from her abdomen glands and clings to the surface on which she runs. She runs home and gives some of her food to the others, who also run out, following her scented trail. So back and forth, they go, leaving a trail for others to follow. When they meet along the way, they're probably saying in ant language, "HI SIS! YOU'RE ON THE RIGHT TRACK! KEEP IT UP!"