Epsilon

noun

1. The name for the fifth letter of the Greek alphabet, ε or Ε, preceded by delta (Δ, δ) and followed by zeta (Ζ, ζ).
2. In IPA, the phonetic symbol ɛ that represents the open-mid front unrounded vowel.
3. An arbitrarily small quantity.
4. A negligible effect.

   "Yes, we have to convert all the symbol names to upper case at startup, but that’s epsilon."

5. The percentage change in an option value with respect to the underlying dividend yield.