The phrase "spectral region" refers to a specific range of wavelengths or frequencies of light. It represents a specific portion of the electromagnetic spectrum. Full definition
Chemical compounds all carry distinctive absorption «fingerprints» within the mid-infrared spectral region of 2 to 12 microns. (sciencedaily.com)
Action spectra for UV - induced erythema, DNA damage, photoimmunesuppression, squamous cell carcinoma and vitamin D synthesis are very similar, all in the UVB spectral region of 280 - 310 nm. (articles.mercola.com)
We retrieve CO2 only over land due to the low reflectivity of water in the near - infrared spectral region used to retrieve CO2 information from the satellite spectra of reflected solar radiation. (esa-ghg-cci.org)