What what means?

Pretty simple. There are a number of apps available for smartphones and a number of websites you can upload a barcode image to that will translate the barcode into whatever text (yes, a barcode is just a way to encode text into a machine-readable format) was used to create the barcode.

Pretty simple...but I will be happy to expand on it if you need this interpreted, too.

The whole two-part system of "reservations and tickets" is really a relic of the ancient days of travel--before electronic ticketing became popular. You needed a reservation so the airline knew you were coming and didn't sell too many seats on a given aircraft. Your travel agent would contact the airline and place the reservation for your seat. However, the reservation didn't have any intrinsic value in and of itself. You would pay your travel agency for the flight, and they would then issue you a paper ticket which did have intrinsic value, and you were required to carry that ticket to the airport (where you would obtain a boarding pass, which referenced the fact that you had a reservation for that flight) and surrender it when boarding your flight. The airline's accounting department after the fact would then settle the tickets and deal with exchanging money between itself and the travel agencies.

With the advent of CRSes (computer reservation systems) and the installation of GDS terminals in travel agencies around the world, the process of finding flights and placing reservations was streamlined a great deal, but you still had to pay your travel agent and get a paper ticket issued to provide when boarding (remember the boarding passes that said "FLIGHT COUPON REQUIRED"?), which the airline's accounting department then settled against the electronic reservation record.

Then, a couple of decades ago, the concept of the e-ticket came about, and the ticket details then remained stored in an electronic record. Still, aside from not having to physically present the ticket during the boarding process, the process remains the same: the reservation is created, the ticket is issued, the boarding pass is created, and then after the flight, the ticket is settled against the reservation.

Really, though, there's no reason there needs to be so many steps. It is this way because the airlines are still using the same 1960s-era mainframe-based legacy CRSes they always have, and it was a lot simpler and cheaper to modify the existing systems to deal with electronic records than to overhaul the entire system. All of the steps of the process you see during a modern day airline transaction correspond directly to manual steps of the process in the olden days. For more on that, check this thread out and read the next four posts.

If someone were creating an airline from scratch in the modern era (and didn't have to worry about integrating it with other, existing carriers and the messes created by interlining and codesharing and plating a ticket on one carrier for a flight on a different carrier and all of that), it would actually be fairly simple to program a system that just lets you book a flight. You'd receive a receipt that shows you're booked on the flight, and a quick verification of the receipt's validity would let you get on the plane. You could entirely skip the whole process of issuing a ticket and generating a boarding pass and ensuring that the reservation data and ticket data are in sync and all of that. That would be a ticketless system. But it would represent a wholesale change in the way the reservation system works, and I'm pretty confident Amtrak didn't reinvent the wheel. (We would know about it if they did.)

This is likely what actually happens. There's no real need anymore for the customer to know about or care about the ticket number. The conductors' iPhones are programmed to pull up the customer's record by the reservation number, and behind the scenes, ARROW then checks to ensure a valid ticket is attached to the reservation and allows the conductor to virtually "lift" the ticket.