What is the difference between a blackbody and a graybody?

A blackbody is an ideal surface that absorbs all incident radiation regardless of wavelength and direction, with emissivity ε = 1. It emits the maximum possible radiation at any given temperature. A graybody is a more realistic model where emissivity is constant across all wavelengths but less than 1 (0 < ε < 1). Real surfaces are often approximated as graybodies for engineering calculations. Examples: lampblack (ε ≈ 0.95) behaves nearly as a blackbody, while polished aluminum (ε ≈ 0.05) is far from it.