What is heatmap in SEO. Does anyone give me brief explanation about this.

A heatmap is a way to analyze your site with a visual "graph" if you will. It will track the clicks across your site and let you see visually where on the page most clicks are made. Red usually indicating highest quantity of clicks per area.

Here is an example of an heat map, http://www.searchenginepeople.com/i/wp-content/uploads/2007/11/clickheat-screenshot.png.