A vigneron is a 'grape grower', someone who owns and takes care of vineyards. Pruning, maintaining the vines: it's all done to make sure the grapes are in good condition by the time they are picked. Historically, Champagne has many vignerons who sell off their vintage to the large domaines, the 'grandes marques'.
Nowadays, more and more grape growers chose to use their vineyards, which in many cases have been in the family for generations, for producing their own wines: these are called 'vigneron-' or 'grower champagnes'. The champagnes we import come from vignerons, families with just a few hectares of land, who do not buy any fruit from others.