This holiday commemorates the Exodus from Egypt. If you've seen Cecil B. DeMille's "The Ten Commandments," then you know the story of Passover, more or less. Passover is celebrated for seven or eight days (depending on your branch of Judaism) starting on the night of a full moon in April. Passover usually overlaps with Easter, though occasionally Passover occurs a month after Easter.
Almost all American Jews observe Passover to some extent, even if only to go to their parents' house for a ritual dinner (called a seder, pronounced SAY-der) on the first and/or second night of the holiday. Most (though not all) American Jews avoid bread and grain products to one extent or another throughout this holiday, in memory of the fact that our ancestors left Egypt in a hurry and didn't have time to wait for their bread to rise. You should avoid scheduling events involving food during this holiday, and should avoid scheduling travel for Jews because it may be hard for them to find suitable food away from home.
Strictly observant Jews do not work, go to school or carry out any business on the first two and last two days of Passover (first one day and last one day for some branches). This is a requirement of Jewish law; however, only about 10% of the American Jewish population observes this rule strictly. Most American Jews will work through Passover, although many may want to take time off the day before Passover, to prepare for the big family dinner. To put this in perspective: imagine if you had to work during the day of Thanksgiving, then prepare for Thanksgiving dinner after getting home from work.
Remember that Passover, like all Jewish holidays, begins the evening before the date that it appears on your calendar. If your calendar says that Passover starts on April 24, then Passover really begins with the family dinner on the night of April 23.