Liferay Portal

 Web application is an application that is accessed over a network such as the Internet or an intranet.
 A portal application is a web application that can coexist with many other applications in a civilized way and also that can leverage functionality provided by the portal platform to reduce development time and deliver a more consistent experience to end users.

Portlets: portlets are small web applications written in Java that follow a certain set of rules to allow cohabitation within the same portal or even within the same page. Portlets can be used to build applications as complex as you want since the full suite of technologies and libraries for the Java platform can be used.

OpenSocial Gadgets: gadgets are usually small applications, written using browser side technologies such as HTML and Javascript. One interesting benefit of gadgets is that they are easy to develop and for that reason there are thousands of them in repositories such as iGoogle’s repository. When the application becomes more complicated you will need a complementary backend technology, such as portlets or regular Java web applications.

What makes Liferay Portal unique

Liferay Portal is a web experience platform that contains all of the common applications you’d use as building blocks for your web site. Because of this, using Liferay completely changes the way you’d approach building your site, because Liferay includes all the functionality mentioned above and more. In fact, depending on what you’re building, it’s possible to build some sites without writing any code at all! If you’ve got a great application in mind, then Liferay is also a fantastic web application development platform that you can use to your advantage to release your application faster. Why? Because you can focus on your application, and use the user management, security, standards support, and general features provided by Liferay Portal without having to write them yourself.