Translucent
A translucent material lets some light through but scatters it, so objects behind it appear blurry, like frosted glass or wax paper.
Definition
A translucent material lets light through but mixes it up so clear shapes on the other side cannot be seen, such as frosted glass, wax paper, or a thin sheet of paper, giving light without a clear view; a bathroom window of frosted glass lets in daylight but blurs everything, sitting between transparent and opaque. It transmits light but scatters it in many directions as it passes through, so light emerges diffused and images behind it appear blurred or invisible, the scattering coming from internal surfaces, tiny particles, or a rough texture, which is useful for spreading light evenly in lampshades and frosted bulbs. Translucency arises from multiple scattering, where refractive-index variations on a scale comparable to or larger than the wavelength (grain boundaries, pores, particles, fibers) redirect light without absorbing it; particles much smaller than $\lambda$ scatter by Rayleigh's $\lambda^{-4}$ law while larger particles follow Mie theory with weak wavelength dependence, which is why milk and clouds look white, and transmitted light splits into a ballistic component that preserves direction and a diffuse component that does not, with the ratio depending on thickness and the scattering mean free path.
Example
A sheet of tissue paper held over a flashlight passes perhaps $60\%$ of the light, but the beam that comes out is a soft glow instead of a spot, and stacking five sheets drops the transmitted light to a small fraction as each layer scatters and absorbs more. Skim milk looks bluish while whole milk looks white, since fewer, smaller fat globules favor Rayleigh-type scattering of short wavelengths while whole milk's larger, more numerous globules scatter all colors nearly equally, and a drop of milk in a tank of water lit by a flashlight reproduces a blue sky from the side and an orange sunset straight through.
Key Insight
Clouds are translucent water: each droplet is transparent, but billions of them scatter light so many times that the Sun becomes a bright blur and the cloud glows white from every side. Human tissue is translucent in the red and near-infrared, which is why a flashlight pressed against fingers glows red and why pulse oximeters and some brain imaging methods can read what is happening inside without cutting anything open.