The Mod bar is an area down the left hand side of each module defining the available functions. A typical mod bar is illustrated below as in enCentral:
Modbar on left of enVisual module
Normally the mod bar is shown, but it can be hidden by double clicking on the column on the far left hand side containing the title of the module (in this case enCentral - CRM). The mod bar will then be retracted and hidden. To unhide the mod bar double click the far left column again and it will once again appear.