Dictionary.net

A term which describes a system that dealscorrectly with extended character sets which (unlike ASCII)use all eight bits of a byte. Many programs andcommunications systems assume that all characters have codesin the range 0 to 127. This leaves the top bit of each bytefree for use as a parity bit or some kind of flag bit.These assumptions break down when the program is used in somenon-english-speaking countries with larger alphabets.If a binary file is transmitted via a communications linkwhich is not eight-bit clean, it will be corrupted. To combatthis you can encode it with uuencode which uses only ASCIIcharacters. There are some links however which are not even"seven-bit clean" and cause problems even for uuencoded data.