In Bordeaux, the French word "cru", or growth, is used to indicate a wine estate, vineyard, or chateau. Thus a Premier Cru, or First Growth, is a wine estate of the top (first) rank.
According to THE WINE BIBLE, by Karen MacNeil, among the Firth Growths, Margaux and Lafite-Rothschild are often the most elegant and subtle; Haut-Brion, the most earthy; and Mouton-Rothschild and Latour, the most powerful.