Landing pages are simply a specific website page that is used for a specific campaign or conversion objective.
For example, if you have a call-to-action (CTA) on your website, you are asking web users to take a certain action by click on your CTA; Perhaps you would like them to click on your CTA to download an e-book or whitepaper. They would be taken to a landing page when they click the CTA so that they may complete the process of the intended action.
There is an art to optimizing a landing page and conventional wisdom calls for a landing page to be used for one (1) purpose only. If you want that user to download an e-Book or whitepaper, then don't confuse them with additional options.