The term “Meter” is not commonly used in music copyright opinions. Fisher v. Dees (1986) does briefly refer to this term in the court’s discussion of a parody’s need to imitate quite closely the “music or meter” of an underlying work for the parody to be effective.
Meter refers to the regular grouping of Beats within the larger unit of a musical Bar or Measure. Meters are determined by the number of Beats -- steady rhythmic pulses -- comprising a single measure. In “Yankee Doodle” each Bar, including the fourth Bar that has only two notes and syllables (“po-ny”), has four beats. Because four is a multiple of two, we say this song has a “duple” Meter. Typically the first beat of a measure in any particular meter is given a slight emphasis – volume or duration – indicating its structural preeminence in the measure.