The word lock has several meanings:

1. A device that keeps doors, boxes, or other things securely closed. Most locks need a specific key or combination to open them. You might use a padlock to secure your bike, turn a deadbolt on your front door at night, or spin the dial on a combination lock at school. Locks work by blocking something from moving until you provide the right key or code. Before locks were invented, people had to guard their valuables constantly or hide them.
2. To fasten or secure something with a lock. When you lock a door, you're making sure it stays closed and that only people with keys can open it. You can also lock things without an actual lock device: wrestlers lock their arms around opponents, and you might lock your fingers together when you clasp your hands.
3. A section of a canal where water levels can be raised or lowered to move boats between different heights. Canal locks work like water elevators, filling with water to lift boats up or draining to lower them down. The Panama Canal uses massive locks to help ships travel between the Atlantic and Pacific Oceans, which are at different elevations.
4. A small section of hair that hangs together. Parents sometimes save a lock of their baby's hair as a keepsake.