Could someone explain to me what is 'Evergreen' game in chess.?Thanks.

I think it is the game played in 1852 between Adolf Anderssen and Jean Dufresne.

This and the "Immortal Game" demonstrate Anderssen's amazing tactical abilities. 

A move by move description can be found at

http://en.wikipedia.org/wiki/Evergreen_game

Evergreen, is a conifer tree it stays green all years round.