ðə tˈɜːm ɪz kˈɑːmənli jˈuːzd ɪn ɐbsˈoːɹpʃən spɛktɹˈɑːskəpi, kˌɔːɹɪspˈɑːndɪŋ tʊ ɐ wˈeɪvlɛŋθ ʌv mˈæksɪməm ɐbsˈoːɹpʃən ɪlˌɛktɹoʊmɐɡnˈɛɾɪk ɹˌeɪdɪˈeɪʃən ɹˈeɪndʒɪŋ ɚɹˈaʊnd fˈoːɹhˈʌndɹɪd ˌɛnˈɛm ɪnðə blˈuː ɹˈiːdʒən.
The term is commonly used in absorption spectroscopy, corresponding to a wavelength of maximum absorption (electromagnetic radiation) ranging around 400 nm in the blue region.