The practice and the study of designing very small electrical circuits — the kind inside phones, computers, cars, and almost every modern machine. If someone studies microelectronics, they learn how to design and build things at that tiny scale. It is a technical, university-and-factory word. In everyday talk, people just say chips or electronics. Like physics or economics, the -s names a field, not a pile of countable things: microelectronics is, not are. Though actually, the circuits are small, but the industry is not: whole countries, including Taiwan, are famous for this work.