Two women enjoy sakura in Tokyo.
Hanami is the traditional Japanese custom of viewing blooming sakura, cherry blossoms. Japanese people gather under trees and bring sake and snacks to eat. When the wind blows the falling cherry blossoms, everyone goes "Ohhhh!". People enjoy each others company, drink sake together and enjoy the amazing white blossoms.
Hanami is usually in end of March or the very beginning of April when sakura is fully blooming. In Hokkaido, sakura is blooming much later, so hanami season can be almost one month later there. In southern Japan sakura's blossoms are fully blooming is more early. Typical locations to keep Hanami party in Tokyo area would be Ueno Park or Shinjuku Koen. However during best hanami time, these locations get very crowded.
Cherry blossom viewing during night time is called yozakura. During night time the beauty of sakura is altogether different kind of experience. The colour of sakura seems very different.
Hanami, or sometimes hanami matsuri (festival) has long tradition. Shikibu Murasaki's Tale of Genji described similar kind of flower viewing. Hanami originally was used for announce the rice-planting season. Also there are lot of beliefs related to sakura trees. It is a symbol of purity, and spiritual energy, and sometimes a sign of gods mercy. Weddings are often kept in the time when sakura is blooming and petals of sakura are literally raining from the trees. There are plenty of haiku poems which describe hanami events.
It is often said that Hanami describes life itself as season of cherry blossom is so short and fleeting. Hanami is also a good symbol of aesthetical nature of Japanese mind.