HTTP uses the same definition of the term "character set" as that described for MIME:
Note: This use of the term "character set" is more commonly referred to as a "character encoding." However, since HTTP and MIME share the same registry, it is important that the terminology also be shared.
HTTP character sets are identified by case-insensitive tokens. The complete set of tokens are defined by the IANA Character Set registry . However, because that registry does not define a single, consistent token for each character set, we define here the preferred names for those character sets most likely to be used with HTTP entities. These character sets include those registered by RFC 1521  -- the US-ASCII  and ISO-8859  character sets -- and other names specifically recommended for use within MIME charset parameters.
charset = "US-ASCII" | "ISO-8859-1" | "ISO-8859-2" | "ISO-8859-3" | "ISO-8859-4" | "ISO-8859-5" | "ISO-8859-6" | "ISO-8859-7" | "ISO-8859-8" | "ISO-8859-9" | "ISO-2022-JP" | "ISO-2022-JP-2" | "ISO-2022-KR" | "UNICODE-1-1" | "UNICODE-1-1-UTF-7" | "UNICODE-1-1-UTF-8" | token
Although HTTP allows an arbitrary token to be used as a charset value, any token that has a predefined value within the IANA Character Set registry  must represent the character set defined by that registry. Applications should limit their use of character sets to those defined by the IANA registry.
The character set of an entity body should be labelled as the lowest common denominator of the character codes used within that body, with the exception that no label is preferred over the labels US-ASCII or ISO-8859-1.