Final answer:
The major system used in the US is English units, also known as the imperial system. Virtually every other country in the world now uses the SI units (acronym for the French Système International d'Unités), also known as the metric system, which is the standard system agreed upon by scientists and mathematicians.
Step-by-step explanation:
The major system used in the US is English units, also known as the imperial system. The English units were historically used in nations once ruled by the British Empire and are still widely used in the United States. Virtually every other country in the world now uses the SI units (acronym for the French Système International d'Unités), also known as the metric system, which is the standard system agreed upon by scientists and mathematicians.