Unicode Transformation Format-8 (UTF-8)  is a byte lossless encoding of Unicode characters.

UTF-8 encodes each Unicode character as a variable number of 1 to 4 octets, where the number of octets depends on the integer value assigned to the Unicode character. It is an efficient encoding of Unicode documents that use mostly ASCII characters because it represents each character in the range U+0000 through U+007F as a single octet.

The UTF-8 is defined as a standard in RFC 3629. You cah find useful UTF-8 FAQ at the Unicode Web site.

UTF-8 is the default encoding for XML.