Hi vani ,
Rittik is right...html site maps is just created webpage which contains all the website url i.e Home page, about us, products etc...which help visitor to find everything (contents of your website) on the one page...
The basic difference between is the file types. Generally any search engine spider would look for the xml sitemap. Even for Google Web master tools, the prescribed format is xml sitemap. Html or text sitemap would be giving the overview of the linkages in the website. Ror format is for websites built in Ruby On Rails.
