Cultures that are associated with a language but are not specific to a country/region. The names of .NET Framework cultures consist of the lowercase two-letter code derived from ISO 639-1. For example: "en" (English) is a neutral culture.
Custom cultures can have any user-specified name, not just a two-letter code.
The invariant culture is included in the array of cultures returned by the CultureInfo.GetCultures(CultureTypes) method that specifies this value.