They were those immigrants who were financially able to retain their base land grant or perhaps enlarge upon it, becoming free landholders with voting rights beginning one Manticoran year (1.73 T-years) after their arrival on the planet. The contrast was to 'zero-balancers' who arrived essentially without resources other than their personal skills.
While all Manticoran citizens were equal before the law, whether enfranchised to vote or not, there were distinct social differences between shareholders, yeomen, and Zero-balancers.. During the centuries, there was always greater prestige in claiming a yeoman as a first ancestor than a zero-balancer. Of course direct descent from a full shareholder was the most prestigious of all three. (UHH, "House of Steel")