Greek Letters in Code

The Greek letter lambda (λ) is pronounced "LAM-dah" /ˈlæmdə/ — two syllables, stress on the first, and the "b" is silent. So "a LAM-dah function", "AWS LAM-dah", "lambda calculus." Do not pronounce the "b" ("lam-BDA") or stress the second syllable. The short /æ/ vowel as in "cat" is correct. This is the most common Greek letter in programming, used for anonymous functions across many languages.

The Greek letter sigma (Σ / σ) is pronounced "SIG-mah" /ˈsɪɡmə/ — two syllables, stress on the first, with a hard "g" /ɡ/ as in "go." So "the SIG-mah notation", "sum over SIG-mah." Uppercase Σ denotes summation; lowercase σ denotes standard deviation in statistics. Do not use a soft "g" ("SIH-jmah") or stress the second syllable. The short /ɪ/ vowel as in "sit" is correct.

The Greek letter epsilon (ε) has two main pronunciations: American "EP-sih-lon" /ˈɛpsɪlɒn/ (stress first) and British "ep-SY-lon" /ɛpˈsaɪlən/ (stress second, long "i"). Both are correct. So "within EP-sih-lon", "a small epsilon." In code and numerics, "epsilon" denotes a tiny value (e.g. machine epsilon, learning-rate epsilon). Do not stress the final syllable. Choose the US or UK form and be consistent.

The Greek letter delta (Δ / δ) is pronounced "DEL-tah" /ˈdɛltə/ — two syllables, stress on the first, short /e/ vowel as in "bed." So "the DEL-tah", "compute the delta", "a delta of 5." In code, "delta" means a change or difference between values (e.g. git diffs, deltas in a stream). Do not stress the second syllable or lengthen the vowel ("DEEL-tah"). It matches the everyday word "delta" (as in a river delta).

The Greek letter mu (μ) is pronounced "mew" /mjuː/ in American English or "moo" /muː/ in British English — one syllable. The symbol μ is the "micro" prefix (e.g. μs = microseconds, "MEW-seconds" or "micro-seconds"). So "the mu symbol", "a few mu-seconds." Both /mjuː/ and /muː/ are accepted. Often in tech speech people just say "micro" rather than "mu" (e.g. "microseconds"). Do not spell it out as "em-you."