Q. What are the Rendered, Rerendered and Renderas in Visualforce page?
Ans:
Render : It's a Boolean value, It works like “display” property of CSS. Used to show or hide element. (if it is true, it displays the block else it will be hidden)
Rerender: After Ajax which component should be refreshed. For this you need to assign id to field, sections or a block. it's available on commandlink, commandbutton, actionsupport etc.
RenderAs: Render visualforce page as pdf, doc or excel.