What is lightning?

(Apex)

Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions in the atmosphere or ground temporarily equalize themselves, causing the instantaneous release of as much as one billion joules of energy.

Lightning component is a client-server framework that accelerates development, as well as app performance, and is ideal for use with the Salesforce1 mobile applications. It uses jа vascript on the client side and Apex on the server side.