An entry page is essentially the page that the user first visits in order to access your website. Therefore, if a landing page of yours is ranking high for a specific term, that landing page may serve as an entry page for a wide variety of users, as they are entering your website via that pages snippet in the search results.
The same applies for pay per click ads, it’s critical that you send the users to the appropriate page on the first click to increase the chances of them converting. An entry page is the first representation of your site, you need to make sure that the user has the right information on the page, relevant to the search query that they typed into the search results, otherwise, they will most likely exit your site.
On the other hand, it’s important to take into consideration the entry page from a link building perspective too, both internally and externally. Not only do you need to ensure that the anchor text is relevant, you need to take into consideration whether or not the information on the page is relevant to the context of the link, to not only help users but search engines too.