Greek letters in science and maths
Many Greek letters have standard meanings. π is the famous circle constant, Δ often means a change in a value, Σ marks a sum, and λ stands for wavelength in physics. Ω is the symbol for ohms, μ means micro, and θ is a common name for an angle. Copying the real character looks far more professional than typing a spelled-out name.
Look-alike letters to watch for
Several Greek capitals look exactly like Latin letters: Α, Β, Ε, Η, Ι, Κ, Μ, Ν, Ο, Ρ, Τ, Χ, Υ and Ζ. They are different characters behind the scenes, so search engines and spell-checkers treat them differently. Use the Greek version only when you mean Greek, and be aware that ς is the special form of sigma used at the end of a word.