Unicode defines two mapping methods:

• the Unicode Transformation Format (UTF) encodings, and
• the Universal Coded Character Set (UCS) encodings.

An encoding maps (possibly a subset of) the range of Unicode code points to sequences of values in some fixed-size range, termed code units. All UTF encodings map code points to a unique sequence of bytes. The numbers in the names of the encodings indicate the number of bits per code unit (for UTF encodings) or the number of bytes per code unit (for UCS encodings and UTF-1). UTF-8 and UTF-16 are the most commonly used encodings. UCS-2 is an obsolete subset of UTF-16; UCS-4 and UTF-32 are functionally equivalent.