A locale category is a particular grouping of language-specific and cultural-convention-specific data. For instance, data referring to date-and-time formatting, the names of the days of the week, names of the months, and other time-specific information is grouped into the LC_TIME category. Each category uses a set of keywords that describe the particulars of that locale subset.
The following standard categories can be defined in a locale definition source file:
| LC_COLLATE | |
| Defines character-collation or string-collation information. | |
| LC_CTYPE | |
| Defines character classification, case conversion, and other character attributes. | |
| LC_MESSAGES | |
| Defines the format for affirmative and negative responses. | |
| LC_MONETARY | |
| Defines rules and symbols for formatting monetary numeric information. | |
| LC_NUMERIC | |
| Defines rules and symbols for formatting nonmonetary numeric information. | |
| LC_TIME | |
| Defines a list of rules and symbols for formatting time and date information. | |
Note: Locale categories can only be modified by editing the locale definition source file; they should not be confused with the environment variables of the same name, which can be set from the command line.