Of a body about an axis is the sum of the products of its mass elements and the squares of their distances to the axis. principal moments of inertia of a molecule are chosen so that IA ≤ IB ≤ IC.
Green Book, 2nd ed., p. 12 (https://dev.goldbook.iupac.org/files/pdf/green_book_2ed.pdf)
PAC, 1996, 68, 957. 'Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)' on page 983 (https://doi.org/10.1351/pac199668040957)