Variable-width encoding

A variable-width encoding is a type of character encoding scheme in which codes of different lengths are used to encode a character set for representation in a computer. All of the common Unicode encodings are variable-width encodings, e.g. UTF-8 and UTF-16. It's a common mistake to think that UTF-16 isn't, so that's not a good reason to prefer UTF-16 (only its obsolete predecessor UCS-2 is fixed-width).

ASCII is a fixed-width encoding. So are many other legacy encodings, but no modern text encoding.