From the latin "of one's own kind", meaning unique, without precedent, or antecedant.
In this case, the object that this object is based on is not in the wiki yet.
Or it is original research. Ideally the wiki page will cite previous research and development.
The Sui Generis 'label' is a bit of a hack. Ideally the template wouldn't display the text "Based On" if that field is left empty --Sebastien Bailard 05:03, 21 June 2010 (UTC)