From LQWiki

A locale is a object on the system that stores information relevant to localization. Such information stored is formating for numbers, text, times, money, as well as what language to speak, and character encoding to use. The localedef utility is used to create locales. On most systems, the directory /usr/lib/locale holds all system wide locales, and /usr/share/locales holds internationalization text for programs.

Locale is also the name of a command that displays NLS information about your current environment.

• locale display what locales are in current use.
• locale -a display all available system wide locales available.

See locale's documentation for more information.