There are several different kinds of Eurail passes. They usually vary on how long they are valid for travel, or how many countries they are valid for travel in.
Below you'll find a brief rundown on each Eurail pass available for train travel in Europe, and all the options available to you. They're all good deals if you plan on doing a lot of travelling, better than point-to-point train tickets.
Eurail Selectpass: The Eurail Selectpass is ideal if you are only going to be travelling in a few specific countries. For example, instead of buying a pass which covers all of Europe, you could just choose to travel in France, Spain, and Germany and get a cheaper pass. You can choose between 3, 4, 5, and single country passes. If you're travelling in a group,or if you are under 26 years old you can get the Eurail Selectpass Saver or Eurail Selectpass Youth and get a discount!
Eurail Selectpass Information
Eurailpass: The Eurailpass combines travel in every European country which supports Eurail - a total of 17 different countries! The pass is great if you plan on doing some extensive travelling across the continent. I've used it, and it was great. Hassle free, just hop on a train in any direction and you're off. No hassles (though sometimes you need to make a reservation on trains). Click the link below for more info about the Eurailpass, and the Eurailpass Youth!