Segla is the "Second wine" of Chateau Rauzan Segla, 2eme Cru Classe of Margaux in the 1855 classification which is still the reference for all top chateaux from Bordeaux.
Most of the Grands Crus Classes of Bordeaux produce now a "second wine".
A second wine of a Chateau is a wine produced from the same vineyard as the main Chateau and vinified with the same care but made from grapes coming from the younger vines (usually less than 10 years old). The second wine is also aged in oak barrel but for a shorter time than the main label.
This means that Segla has all the characteristics and "finesse" of a great Margaux but will mature quicker and be ready to be drunk earlier.
The total production of Segla is only about 4000 cases per year as against 12000 cases for the first label Chateau Rauzan Segla.
Since the Second wines like Segla cost normally less that half the price of the "first wine" of the Chateau they are very much in demand on the market.