Liferay Portal is the leading open source enterprise Portal Framework using the latest Java and Web 2.0 Technologies. It is the best of breed, over JBoss Portals, Apache Jetspeed and Pluto and more. In fact, Liferay project/product downloads range from 31,000 to over 48,000 downloads each month over the last year; and over 1,223,584 downloads to date, approximately 40% of the total downloads Spring Framework gets on SourceForge.net.
According to Wikipedia, a web portal is a site that provides a single function via a web page or site. Web portals often function as a point of access to information on the World Wide Web. Portals present information from diverse sources in a unified way. An example of a web portal is Yahoo!
Pro Liferay by Dr Sarang is one of the first books on Liferay, and serves as a practical guide to learning Liferay and developing real-world Web 2.0 portals using Liferay.