Greek Letters (α β π Ω)

The practical way is copying them from a page like this. Word also supports typing the Unicode value then Alt+X, and on a Mac you can enable the Greek input source in keyboard settings.

π (pi) for the circle constant, Δ (delta) for change, σ and Σ (sigma) for standard deviation and sums, α β γ for angles and coefficients, λ (lambda) for wavelength and functions, μ (mu) for mean and micro, and Ω (omega) for ohms.

They look identical but Unicode has both: µ (U+00B5, the micro sign, on many European keyboards as AltGr+M) and μ (U+03BC, the Greek letter). Both are here; for measurements either displays fine, but the micro sign is the semantically correct one.

In documents and spreadsheets, yes, paste freely. In code, many languages now allow Greek identifiers, but teams usually avoid them for readability; strings and comments are always safe.