What does Elon Musk mean by "electric jet"?
Jet noun


a rapid stream of liquid or gas forced out of a small opening


A Jet Engine is an Engine which uses a Jet for propulsion. Typically, a "rapid stream of gas", in which the gas is air. Really, we could count pretty much any aircraft engine as a jet, but it depends on how "rapid" you require the air to be before it's a jet.

In a typical jet engine as we define it now, the jet is created by burning fuel and air... but there's no requirement for that to be the case. An electric jet would simply use an electric motor to create a rapid stream of air.

Would it really be a "jet" engine? That depends how fast the air is - but most people see "jet" as being a fast, powerful, reliable type of aircraft, so it's as much about marketing as anything else. An Electric Prop or Electric Plane doesn't sound as cool as Electric Jet... (Although I'd argue that ElectroJet/ElectroProp/ElectroPlane are awesome names and Elon Musk has let himself down by not using one of those names)