\epsilonThe Greek letter epsilon (\epsilon) is commonly used in mathematics and science to represent a small positive quantity, an arbitrarily small positive number, or an error term. It is often used in calculus, real analysis, and other fields to denote a small quantity that can be made as small as desired.
Epsilon-delta definition of a limit in calculus.
\lim_{x \to a} f(x) = L \Rightarrow \forall \epsilon > 0, \exists \delta > 0, \text{such that } |f(x) - L| < \epsilon \text{ whenever } 0 < |x - a| < \deltaEpsilon representing a small positive number.
\epsilon = \frac{1}{n} \text{ for some large } nEpsilon as an error term in approximation.
f(x) = L + \epsilon