Other forms: keeping track; kept track; keeps track
When you stay informed about something or aware of where someone is, you keep track. While you let your dog run loose on the beach, it's your responsibility to keep track of him.
If say you'll keep an eye on your little cousin at the beach, you need to keep track of her. And if you continuously check online to see where your friend's plane is as she travels to India, you keep track of her flight. The opposite of keep track — if you forget, or get too sleepy, or lose interest — is to lose track.