Lock

1. To prevent access to something until unlocked. For example, a user may lock access to the computer to prevent any unauthorized access while he or she is gone.
2. Permanently enable something until disabled or unlocked. For example, the caps lock permanently enables capitalization on the keyboard until it is pressed again.
3. A physical lock on a computer that prevents it or an attached peripheral from being taken.
4. Short for lock up.
5. A small symbol shown when data sent over an Internet browser is secure. See document CH000507 for additional information about this. 

Also see: Security definitions, Unlock