Japan Rail Pass is a special train ticket for foreign tourists.
This Web site explains who is eligible for this ticket, and how and where you can purchase it.

The ticket is valid for all JR trains including Shinkansen Express (bullet trains), except for Nozomi trains. In spite of the name "Rail" Pass, you can also use it for JR bus and ferry. Please refer to http://www.japanrailpass.net/eng/en004.html for more details.

The pricing can be found at http://www.japanrailpass.net/eng/en003.html
The ordinary 7-day Japan Rail Pass costs 28,300 yen for an adult. This is about 4,000 yen per day. Suppose you travel from Tokyo to Shin-fuji (the nearest station to Mt. Fuji) by Shinkansen Express. Without Japan Rail Pass, you would have to pay about 5,000 yen for this 1-hour trip. Japan Rail Pass saves you 1,000 yen for this trip alone, and possibly more if you make another trip on the same day.
Don't miss the most economical way to travel inside Japan.