An e-ticket is a ticket that is stored in the airline's database in electronic form. This form of air ticket is now universally used instead of the ordinary paper form that was common before.

An itinerary receipt is a detailed breakdown of the e-ticket with all the necessary flight information. It serves as proof of air ticket purchase, it is printed out for presentation at the check-in counter at the airport — and based on it, the passenger receives a boarding pass.

An e-ticket has no other physical embodiment except for the itinerary receipt. When you are asked to present an air ticket, they absolutely always mean the itinerary receipt. But remember that boarding the plane is not done with the itinerary receipt, but with the boarding pass, which is issued during check-in.