Standing wave frequencies of a system are called its modes, ranked by order

Evidence

Standing waves in an acoustic context are often called the modes of a given system; the lowest-frequency standing wave is known as the “first-order mode,” and the multiples of this are higher-order modes. So the third-order mode of a system is the third lowest frequency standing wave pattern that can occur in it. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 413

Categorization

• DEFINE: Defines ‘mode,’ ‘first-order mode,’ and ‘higher-order modes’ — foundational terminology for psychoacoustics.
• corroborated: 2 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 413