Then how was Spongetech planning to retire them? share certificate Definition Legal document issued as proof of ownership in a firm. In the modern stock markets, the 'paper' share is now being replaced by the 'electronic' share. <a href="http://www.businessdictionary.com/definition/share-certificate.html#" rel="nofollow" target="_blank">http://www.businessdictionary.com/definition/share-certificate.html#</a>