A digital record of a traveller's ticket purchase, in common use by airlines, that replaces the issuing of a paper ticket. Not a particularly complex or revolutionary thing at the turn of the 21st century, but many people who aren't comfortable with computers (or who don't trust big airlines, which is probably more folks) don't like taking it on faith that an airline's system will remember who paid to fly where and when.
In practical terms, here's how it works: You go to your travel agent and plunk down your money. The agent makes a reservation for you and takes the money. In exchange, you get a receipt and an itinerary. On travel day, you go to the check-in counter, tell them who you are and where you're going (maybe show them the receipt, if you want), and they give you a boarding pass. You get on the plane and you go. Alternatively, depending on the airline, you might be able to buy an e-ticket for yourself through the Internet. Whether you print off the Web page or a travel agent does, the result is the same.
The airlines say that not having to bother with the infrastructure supporting paper tickets saves them as much as US$5 every time an e-ticket is issued. In many cases, airlines have started to charge passengers (as much as US$20) to issue paper tickets on routes where e-tickets are available.
Some passengers like holding paper tickets as talismans against airline incompetence, which is fair enough. They really do just serve as totems, though, physical representations of the information buried in the company's computer: if you ain't in the computerized records, you ain't getting on the plane, whether you have a physical ticket or not.
On Jan. 1, 2003, Air Canada is to become the first airline in the world to move exclusively to e-tickets, according to its corporate bumpf, though the truth is probably more that it's the first traditional airline to do so.