An Acronym for Unicode Transformation Format.
Description of a scheme for storing Unicode code points in some unit of storage. In general, any particular code point may require multiple units of storage to express it. A particular UTF scheme is referenced by accompanying the acronym with the unit's number of bits. An example, and the most common scheme in practice, is UTF-8, which has a number of important advantages over all other UTF schemes.
UTF schemes are used because as of this writing, the full range of Unicode code points is 0x00000-0x10FFFF and requires a minimum of 24 bits to express (in practice, 32 bits are used instead), most of which are never used in most text. UTF schemes thus provide a highly specialized form of efficient compression that still keeps the resultant text easily processible.
See also:
Characters vs. Bytes