The term BI-X FOUR is a combination of two words, 'BI' and 'X FOUR'. The first word, 'BI', stands for 'Binary Input', which is a type of digital input that uses two states, usually 0 and 1, to represent data. The second word, 'X FOUR', stands for 'Octal', which is a base 8 numbering system that uses the digits 0-7 to represent numbers. The combination of these two words, BI-X FOUR, is used to refer to a type of digital input that uses binary and octal numbers.