The Passover Haggadah is a Hebrew narrative that tells the story of the Israelites and their mass-exit or Exodus from their bondage in Egypt. The Passover Haggadah is recited during the Passover ceremonial evening meal (The Seder). Some Haggadahs are beatifully illustrated.
The basic elements of the Haggadah are ancient; they were already deliniated at the time of the Mishnah over two thousand years ago.
Different groups within Judaism are more and less liberal about the format and content of the Passover Haggadah. Conservative Judaism might use Haggadahs that are only written in the Hebrew language and conforms tightly to an early text. Reform Judaism generally finds it perferable to use a Haggadah that has either a Hebrew with a local language translation (such as English), or a local language-only translation so all participants (especially children who might not speak Hebrew) clearly understand everything.
Haggadah books all have a very similar story to tell, they all use the same characters and the same chain of events. They all are all based on the events of the Exodus as described in the Book of Exodus with a religious context, and include words (and sometimes even music) for religious prayer-songs. However, they may explain things in slightly different ways and have different translations for words.