In simple term Liferay Portal
- made easy to create gadgets,portlets,pages,themes.
- is implementation of portal specification (including JSR 168 and 286).
- is web platform through which we can build business solutions.
- provides collaborative tools.
- having 60+ out of the box (Ready to use) portlets.
- provides role based content management (JSR 170 compatible).
- provides multilingual support.
and lot more …… for more info please visit http://www.liferay.com/products/what-is-a-portal/web-platform
I would recommend looking at index page ‘A Complete Liferay Guide‘