You can hide each of the four main tabs - Content, My desk, Tools and Administration - as highlighted in this screenshot:

 

 

As you can see, the CMS Desk module has UI elements with exactly the same names as the tabs above:

 

 

Page url: http://devnet.kentico.com/docs/5_5r2/devguide/index.html?ui_personalization_cms_desk_main_tabs.htm