What is it?
First of all, let's point out that a standard product page contains navigation menu, which allows to navigate the store freely. "Add to Cart" button, price tag and delivery details are also present on the page, along with item description. A typical sight for anybody who is familiar to online stores.
A single product landing page is something different. It is a landing page dedicated solely to a single product of an online store. Product details are the same, but the page and its elements are presented in a very engaging manner that catches your eye. No navigation, no other products, no ads, no menus, in other words — no distractions.
An awesome single product website example from Eldin Heric: