On a calculator display, E (or e) stands for exponent of 10, and it's always followed by another number, which is the value of the exponent. For example, a calculator would show the number 25 trillion as either 2.5E13 or 2.5e13. In other words, E (or e) is a short form for scientific notation.

What does this ∈ mean?

The symbol ∈ indicates set membership and means “is an element of” so that the statement x∈A means that x is an element of the set A. In other words, x is one of the objects in the collection of (possibly many) objects in the set A.

Does E mean exponential?

The letter e is used in many mathematical calculations to stand for a particular number known as the exponential constant. ... The exponential constant is an important mathematical constant and is given the symbol e. Its value is approximately 2.718.