everything glows if you're hot enough — the color just tells on your temperature.
means the light emitted by any object purely because it has heat, with a spectrum that depends only on temperature, not material.
from coined from the theoretical blackbody, an idealized object that absorbs all light hitting it and re-emits it perfectly based on heat alone; physicists in the 1800s built ovens with tiny holes to approximate one and got very confused by what they measured.
cosmic microwave background — 2.7 kelvin afterglow of the big bang, measured by cobe in 1990
tungsten filament bulb — glows yellow-white near 2700 kelvin, classic incandescent light
the sun — surface at 5778 kelvin, peaks in visible yellow-green light
forged steel — blacksmiths judge heat by color, cherry red near 800 celsius