A landing page can be considered to be any page that a visitor can land on once they arrive on a specific site. In terms of advertising or marketing it is considered a stand alone web page that is completely different than the main website.
Landing pages will be designed for one single objective, such as a purchase page or a call to action page. Landing pages are set up to be the first pages that a visitor is routed to on any particular site, so it limits their ability to look for information on that site without first accessing the landing page information that the site wants to convey.
There are different types of landing pages, Click through and Lead Generation, which is also referred to as Lead Generation or Lead Capture pages. Click through pages are built with the goal of persuading the visitor to click through to a specific page whereas lead generation pages are used to gain user data like their names and email addresses in order to market to the person in the future.