The term PREFIX FOR 'WATT' OR 'BYTE' can be solved with the word GIGA, which is a four letter prefix. GIGA is derived from the Greek word for 'GIANT' and is used to denote a factor of one billion. It is commonly used in the fields of computing and electronics to refer to a unit of measurement that is one billion times larger than the base unit. For example, a GigaWatt is one billion watts and a GigaByte is one billion bytes.