You may think that a landing page is where a client clicks first or even your home page. This is partially correct, as it is the page that you land on. But true landing pages have a far far more sinister purpose.
A landing page is pretty much the first page a visitor lands on, but its true reason for being is to keep you there and spend as much time or money on it as humanly possible. Lets say that you have a product XYZ, you want your visitors to look at ONLY that product, you would create a page for it. SEO the daylights out of it and link it to Facebook – Google – Amazon.
If your analytics is set up correctly, you will be able to see which one of these groups stay the longest, which are more interested in your product, and which buy.
On hand of these statistics, you may want to build 3 Landing Pages – adjusting them specifically to your users. i.e. one for Facebook, one for Google, one for Amazon. Bare in mind that clients do not like change (who does), so a good webmaster will try and recreate the landing page so that at least colors and functionality mimic the originating site.
A Landing page is a page, that your visitors are attracted to. and entices them to stay.