Character encoding is the only term narrowly. The encoding consists of a character set, character map, codeset, or code page.

character set

Character encoding is the way that a computer interprets and then displays a file as text. Each encoding has its own set of characters that it can match to the file. For example, the Windows-1252 encoding, used for Western European languages, contains characters like accented vowels that are used in Spanish, French, etc. However, an encoding used for Russian family languages would include characters from the Cyrillic alphabet.

Most encodings use 8 bits to encode a single character, which allows the encoding to contain up to 256 characters.

Unicode is a newer encoding system that uses a significantly different system for character encoding that allows it to surpass the 256 character limit. Over 100,000 characters are currently supported by Unicode/UTF-8.

I assume you're talking about portion of the OSI model that handles character-encoding such as ASCII. It is the Presentation Layer of the OSI model.

American Standard Code for Information Interchange. ASCII is a form of character encoding.