The landing page of a website, is a page on your website that a visitor can arrive on from outside of your homepage directory. The landing page is not necessarily only the home page of a site. Someone could end up on your landing page in a significant amount of ways. For example, a major way a potential customer is directed to your landing page, is simply via clicking one of your ads.
A landing page may also be referred to a standalone web page. This is due to the fact that the main idea of a landing page is to convert your visitor. Which is why there a very limited clickable navigations on a typical landing page. This is to help guide the visitor toward your conversion goal. For example, a conversion on a landing page may be to educate your visitor on your client. Then follow up with a dedicated place for the visitor to "Subscribe to our newsletter to learn more!".
There are two basic forms of a landing page. These two forms are known as Click Through and Lead Generation. A click through page is used to convince the visitor to click over to another page on the website. Typically the page intended for the visitor to click over to, is where the real conversion happens (ecommerce shopping cart). Meanwhile, the lead generation landing page is mainly used to convert the visitor into a potential customer. This is done by having the visitor subscriber to a newsletter, free trial, discount coupon etc.
E.g. “I’m adding a coupon to my landing page so that my website visitors will be encouraged to buy.”