The visual aspect is an optical property of a material. When the material passes almost no light transmission, it classifies as an opaque material. Low to medium light transmission makes a material transclucent. A material is transparent when almost all light that goes into the material is transmitted.
Transparent materials are particularly in high demand for biomedical applications. Not every wavelength can be used to print a high-quality transparent materials; a shorter wavelength (385 nm) is required for this.