What are Render and Rerender in Salesforce Visualforce page ?

Hi Arun

Render:Render is used to hide or display a visualforce component.

<apex:page controller="RenderedControllr">
<apex:form >
<apex:pageBlock >
<apex:commandButton value="Show Bottom Page Block" action="{!ShowBlockMethod}"/>
</apex:pageBlock>
<apex:pageBlock rendered="{!flag}">
Account Name  :<apex:outputField value="{!filedName}"/>
<br/>
Account Number :<apex:outputField value="{!fieldNAme}"/>
</apex:pageBlock>
</apex:form>

</apex:page>

reRendered:It is used to refresh perticular section of vf page.

<apex:page controller="ControllerName">

<apex:form >
<apex:pageBlock >
<apex:commandButton value="Refresh Section" action="{!method}" rerender="one"/>
</apex:pageBlock>

<apex:pageBlock id="one">
<b>  Output Text   : </b>   <apex:outputText value="{!fieldname}"/>
</apex:pageBlock>
</apex:form>

</apex:page>