it means that a component can only be installed one way, the wires should not be reversed. Polarized plugs on some appliances have one blade wider than the other so it can be inserted only one way. Some components have one wire longer than the other to indicate polarity. Some are marked with the correct polarity.
An Electronic Component Distributor can be purchased from a specialist electronics site such as Mouser. Other sites that sell them are Newark and Avnet.
IT is a type of device used for some application
A transistor
a volmeter is a component in circuits which measures voltage.CommentI think you mean 'voltmeter'!
It means that it complies with ALL relevant European community standards.