What is the importance of the 8,000 meter mark in climbing?

From the text:

There are fourteen so-called 8,000-meter peaks: mountains that stand more than 8,000 meters (26,246 feet) above sea level. Although it is a somewhat arbitrary designation, mountaineers have always attached special prestige to ascents of 8,000-meter peaks. The first person to climb all fourteen of them was Reinhold Messner, in 1986. To date, only four other climbers have repeated the feat.