Joomla allows developers/designers to override any HTML that is output by a component or module – rather than change core HTML coding, Joomla enables the creation of HTML overrides.

HTML overrides are added to the template html folder - for example:
\templates\maxbiz2\html\mod_breadcrumbs\default.php

In this case we are overriding the HTML layout for the breadcrumbs module by duplicating the core default file and changing the HTML inside the module and saving to this folder structure.

With Joomla 3.2 we can now also override inside the template administrator side.

For more information –
docs.joomla.org/How_to_override_the_output_from_the_Joomla!_core
docs.joomla.org/J3.2:How_to_use_the_Template_Manager#Creating_Overrides