What each one actually is
A web form is a capture component
A form is fields and a submit button. It can sit on a product page, in a sidebar, in a pop-up or at the end of an article. Its job is narrow: collect enough information to act, and deliver it somewhere useful. Everything that makes a form good or bad is about friction and destination, not about design.
A landing page is a destination
A landing page is a whole page built for one offer and one action. It usually removes navigation and competing links, states a single promise, supports it with explanation and evidence, and asks for one thing. It exists because a visitor arriving from a specific advertisement should not have to search for what they clicked on.
