VisualForce

 Visualforce is a markup language that allows defining user interface components in Salesforce.

This tool which runs o force.com platform. By using page layouts, we can easily configure the User interface. But by using visualforce pages, you can develop your own customized user interface.

Developers define pages through specifying Visualforce markup and a Visualforce controller. The Visualforce tag-based markup language looks and behaves similarly to HTML. 

The markup embeds tags and web-enabled languages like HTML and JavaScript within a single <apex:page> tag.

The Visualforce markup controls what elements appear on the page and how they appear. Visualforce tags correspond to page elements, such as form fields or and images. 

Visualforce can integrate with any standard web technology or JavaScript framework to allow for a more animated and rich user interface. Each page is accessible by a unique URL. 

When someone accesses a page the server performs any data processing required by the page, renders the page into HTML, and returns the results to the browser for display.

Sample Code Used inside the Visualforce Component:

<apex:component >

    <apex:attribute name="height" required="true" type="integer" description="Height for the table"/>

    <table height="{!height}" border="2">

        <tr><td><h1>Infallible Techie</h1></td></tr>

    </table>

</apex:component>