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E, in capitalized form, and e in lower-case, is the fifth letter of the Latin-based alphabet systems, including English. It has several meanings in mathematics.

In pure mathematics:

In applied mathematics:

In deductive logic and set theory:

  • ∃, a backwards E, is a symbol used in logic to denote the existence of an entity in a predicate statement.

In computers and calculators:

  • E can be used in place of "×10^" in scientific notation or engineering notation such that $ 1.9 \times 10^5 $ can be equivalently written $ 1.9 \; \mathrm{E} \; 5 $. This is common on older scientific calculator models.
  • E can refer to an Error in digital computation, usually caused by a division by zero or the evaluation of a function outside of its domain. It can also written "Err", "Error", "NaN", and various other notations as a default expression returned when a computing error occurs.

In Euclidean Geometry:

  • E^2 can refer to the Euclidean space, R^2.