By externalizing data that is culture or region-dependent, a system can run worldwide without the need for recompiling.
Typical culture or region dependent data involves aspects such as:

• Language
• messages
• GUI items
• Help
• Formats
• Currency
• Dates/Times
• Measurements
• Numeric formats
• Postal codes
• Addresses
• Cultural preferences
• Dictionary sort order
• Colours
• Sounds
• Graphics

Internationalization
Internationalization allows software to be adapted to any language and cultural convention, by externalizing those parts of the software that are dependent on language and culture.

Localization
Localization is the process of configuring the externalized parts mentioned above for a particular regional of cultural environment.

I18N
Abbreviation for internationalization.
Might be useful for a pubquiz. The not-so-self-explanatory meaning is derived from the fact that there are 18 characters between the "I" and the "n".

I10N
Abbreviation for localization.
Need I say more...