Padlocks are portable locks usually with a shackle that may be passed through an opening to prevent use, theft, vandalism or harm.
Typical modern padlock with keys
Padlocked door
1884 Central Pacific Railroad of Cal. brass boxcar padlock
Old padlock in Kathmandu
A lock is a mechanical or electronic fastening device that is released by a physical object, by supplying secret information, by a combination thereof, or it may only be able to be opened from one side, such as a door chain.
A typical modern padlock and its keys
Bronze lock in a form of scorpion from Nalanda, India, 10th century.
Medieval Gothic lock, from the 15th–16th centuries, made of iron, in the Metropolitan Museum of Art (New York City)
Drunk man's lock at the bottom (black lock) and a regular modern lock at the top