Open any engineering text and a second alphabet is already there: Δ for change, Σ for sums, Ω on every resistor, μ in every microsecond. Greek letters are technical vocabulary's overflow space - 26 Latin letters were never enough - and knowing the 24 by name is a small superpower for reading papers aloud and writing symbols people can search for.
The 24, and where each one earns its keep
The alphabet runs alpha to omega. Some letters carry entire fields on their backs: λ (lambda) is wavelength in physics, the anonymous function in the lambda calculus, and a serverless brand name; μ (mu) is the micro- prefix in μs and μm, the mean in statistics, and the coefficient of friction; Ω (omega) is the ohm, electrical resistance's own letter, while its lowercase ω is angular frequency. Others are famous for one job - π needs no introduction, θ owns angles and Big-Theta bounds, σ is the standard deviation behind "six sigma" - and a few are famous for being confused: ν (nu) looks like a Latin v, and Ο (omicron, "small o") sits opposite Ω ("big o") in name and in notation.
The final sigma
Sigma is the one letter with two lowercase forms: σ inside a word, ς at the end. λόγος (logos) ends in ς, and it is the same letter as the σ it would be anywhere else - a purely positional rule, like nothing in the Latin alphabet. Text processing that treats ς and σ as different letters breaks Greek search and casing; Unicode encodes both and defines the case-folding between them.
Transliteration: modern vs classical
Romanizing Greek has two traditions, and they disagree on exactly the letters engineers say most. Modern Greek (the ISO 843 / ELOT 743 family) writes β as v and η as i - the pronunciation shifted centuries ago. Classical romanization, the one baked into English scientific vocabulary, writes β as b and η as e: that is why the letter called "beta" transliterates to v in a modern Athens street name but gave us the word alphabet with a b. φ is f (classically ph, hence philosophy), χ is ch (the X in Xmas is this letter, not the Latin X), υ fathered no fewer than four Latin letters: U, V, W and Y.
A converter that silently picks one scheme is guessing on your behalf; the Greek alphabet explainer shows the modern form with the classical in parentheses wherever they differ.
Typing it
Every letter here is plain Unicode from the Greek and Coptic block (U+0370 to U+03FF), with accented forms in Greek Extended. Accents decompose: ά is α plus a combining mark, which is why the tool strips combining accents before lookup - άλφα resolves letter by letter to alpha, lambda, phi, alpha, and transliterates to alfa. The right way to write μs in a document is the real μ, not a u that hopes for the best.