slot is a dynamic block

layout/main:

<div id="header"> %% slot header This is the default header %% end </div> <div id="content"> %% slot content This is the default content %% end </div> <div id="footer"> %% slot footer This is the default footer %% end </div> --EOF--
look inside...
Thus Spake Andy:

A slot is a block that can be re-defined by a caller. It's analogous to the way that objects can re-define methods implemented by their base classes. This example shows a typical layout template. We have three slots called header, content and footer and provide some default content for them. We could process this template as it is and we would see the default content generated.