a letter, figure, or other conventional mark naming or referring to an object, quantity, operation, function, etc., as in mathematics:In mathematics, xis often the symbol for an unknown amount. WordReference Random House Unabridged Dictionary of American English © 2024 ...
Spectral dimensions are more conveniently described in terms of wavelength (angstroms), where 1 angstrom is equivalent to 10–7 mm. The electromagnetic spectrum includes radio-frequency waves, light waves, microwaves, infrared, X-rays (Roentgen rays), and gamma rays. 3. The ordered array of ...