Param Tag In VF Page

<apex:param>

A parameter for the parent component. The < apex:param > component can only be a child of the following components:

• < apex:actionFunction >
• < apex:actionSupport >
• < apex:commandLink >
• < apex:outputLink >
• < apex:outputText >
• < flow:interview > so it work in between these tags only

With the help of param component, we can also define date format as below

<apex:page standardController="Account">
  <apex:outputText value="{0,date,dd MMMMMM yyyy}">
        <apex:param value="{!Account.SLAExpirationDate__c}" />
    </apex:outputText>
</apex:page>