The term 'prefix with watt' refers to the prefixes used to denote a multiple of the unit of power, the watt. Giga (4 letters) is a prefix meaning one billion, tera (4 letters) is a prefix meaning one trillion, kilo (4 letters) is a prefix meaning one thousand, and mega (4 letters) is a prefix meaning one million. Therefore, when combined with the watt, these prefixes indicate a multiple of one billion, one trillion, one thousand, and one million watts respectively.