What defines a "triple meter" in music?

A "triple meter" in music is characterized by the grouping of beats into threes, where typically the first beat of the group is the strongest and accented, followed by two weaker beats. This creates a distinctive rhythmic feel, often associated with styles such as waltzes or certain folk dances, where the emphasis on the first beat helps establish a clear sense of moving forward through the measure.

In this context, it's essential to recognize how the accents work within the meter. The pattern of strong-weak-weak provides a flowing and often dance-like quality, which is unlike other meters such as duple meter (where beats are grouped in twos) or quadruple meter (where beats are grouped in fours).

The other options do not correctly define a "triple meter." Grouping beats into four pertains to quadruple meter; stating that every beat is played softly does not address the structural grouping of beats; and using only three different pitches concerns melodic composition rather than rhythmic structure. Thus, the understanding of triple meter relies fundamentally on the grouping of beats and their accents, making the definition in the chosen answer accurate and relevant to musical theory.