What is Passover? Where does the word come from?

The Seder is the special meal that celebrates Passover

Passover (from Pesach or Pesah in Hebrew) is a key festival in Judaism. It commemorates the exodus of the Jewish people from Egypt. This epic story is  told in the Book of Exodus, Chapter 12 of the Torah (the first five books of what Christians refer to as the Old Testament).

Passover is celebrated by friends and family by a special meal known as the seder. During the seder the story of the exodus from Egypt is read aloud from a Hebrew text called the Haggadah (telling). Rituals are acted out at key moments in the story.

Read more - words associated with Passover & Easter 
See here for a short summary of Passover traditions.