A position in an organisation with duties or trusts attached to it; for example, a Government Minister is said to be "in office"; hence "Officer" (a person who holds an office) of "Term of office"
An office is a room or area designed to make administrative work easier in companies and organizations, and was first used for the place where the duties of an office (see above) are conducted for the person who bears those responsibilities; more lately, the meaning has widened.