Learn in the textbookOptical Disc Storage Media — CD, DVD, Blu-ray
DefinitionA Blu-ray Disc (ブルーレイディスク, BD) is an optical disc that uses a blue-violet laser to raise recording density, holding about 25GB per layer on a 12cm disc.
ExplanationThe shorter a laser's wavelength, the finer it can be focused, so switching from the DVD's red to a shorter blue-violet wavelength lets the recorded marks shrink and sit closer together. With two layers it reaches about 50GB, used for high-definition video and large data. BD also comes in types such as read-only BD-ROM, write-once BD-R and rewritable BD-RE.
Memory hookBlu-ray comes from "blue ray", naming the disc after the colour of the laser it reads and writes with.