Eta

Eta (uppercase/lowercase Η η) is a letter of the Greek alphabet. In very early Greek writing it stood for the consonant sound "h", but in Classical Greek it stood for a long vowel "e". In Modern Greek, it is pronounced as "i". In the system of Greek numerals, it has a value of 8. Letters that came from it include the Roman H and Cyrillic И.

Greek alphabet
Αα Alpha Νν Nu Ββ Beta Ξξ Xi Γγ Gamma Οο Omicron Δδ Delta Ππ Pi Εε Epsilon Ρρ Rho Ζζ Zeta Σσς Sigma Ηη Eta Ττ Tau Θθ Theta Υυ Upsilon Ιι Iota Φφ Phi Κκ Kappa Χχ Chi Λλ Lambda Ψψ Psi Μμ Mu Ωω Omega
History
Archaic local variants Diacritics Ligatures Numerals ϛ (6) ϟ (90) ϡ (900)
Use in other languages
Bactrian Coptic Albanian
Related topics
Use as scientific symbols
Book Category Commons

In mathematics, the lowercase η is used to represent Dirichlet eta function.[1] The same letter is also used to represent conformal time in cosmology, efficiency in telecommunications and elasticity in economics.[2]