App vs. Web
An application is, technically speaking, the same as an application: a computer program sold as a product. But applications are designed for small screen devices such as iPhone and Android phones, and then extended to the tablets.
They evolved mostly limited in purpose (a function, or a few closely related functions); They are very easy to use; and cheap: either free or sold for a few dollars.
Many websites are very similar to applications (and vice versa). For example, the website of your bank allows you to view your statements, pay bills, make deposits with pictures of checks, and more. And probably these functions can be done through the implementation.
However, applications are not exactly the same websites. Many websites are only information or information-mostly, with only a bit of functionality – as a simple way of filling to join a mailing list. Other cases, websites can do the same, or some other more complex tasks.
