Ε (Epsilon) is the fifth letter of the Greek alphabet, represented by the symbol "Ε" in uppercase and "ε" in lowercase. It has a numerical value of 5 in the Greek numeral system. Epsilon is often used in mathematics and science to denote small quantities or errors, particularly in calculus and physics. In addition to its mathematical significance, Epsilon appears in various fields, including engineering and computer science. It is also used in the names of certain scientific concepts, such as Epsilon-delta definitions in calculus, which help explain limits and continuity.