An ordered sequence of one or more code units.

• When the code unit is an 8-bit unit, a code unit sequence may also be referred to as a byte sequence.
• A code unit sequence may consist of a single code unit.
• In the context of programming languages, the value of a string data type basically consists of a code unit sequence. Informally, a code unit sequence is itself just referred to as a string, and a byte sequence is referred to as a byte string. Care must be taken in making this terminological equivalence, however, because the formally defined concept of a string may have additional requirements or complications in programming languages. For example, a string is defined as a pointer to char in the C language and is conventionally terminated with a NULL character. In object-oriented languages, a string is a complex object, with associated methods, and its value may or may not consist of merely a code unit sequence.
• Depending on the structure of a character encoding standard, it may be necessary to use a code unit sequence (of more than one unit) to represent a single encoded character. For example, the code unit in SJIS is a byte: encoded characters such as “a” can be represented with a single byte in SJIS, whereas ideographs require a sequence of two code units. The Unicode Standard also makes use of code unit sequences whose length is greater than one code unit.