Definition of unit rule in English:

unit rule

noun

US Politics
  • A procedure for allocating votes that obliges all of a state's representatives to vote the same way, typically for a candidate supported by the majority of constituents.

    Originating in national conventions for the Democratic Party during the 19th century, the term has since been applied in other contexts, most prominently to voting in the electoral college, where the procedure is used by 48 states and the District of Columbia.

Origin

Mid 19th century.