The lower-case letter ε has a number of uses in maths and sciences, such as:
- in analytical chemistry: εi, molar attenuation coefficient, also known as the molar extinction coefficient and molar absorptivity
- in astronomy: the fifth brightest star in a constellation. For instance, Alnilam is designated as ε Orionis.
- in calculus: (ε, δ)-definition of limit
- in medicine: ε-wave, a feature of electrocardiograms of many arrhythmogenic right ventricular dysplasia (ARVC) patients
- in organic chemistry: ε, the fifth atom in a chain when counting from a functional group. The names such as ε-aminocaproic acid make use of this nomenclature.
- in phonetics: Latin epsilon, ɛ, representing the open-mid front unrounded vowel
- in physics: ε0, vacuum permittivity constant