You can call a lot of things a web app, but there are ones that you absolutely shouldn't make with PHP & jQuery, you will hit a point where that architecture be

You can call a lot of things a web app, but there are ones that you absolutely shouldn't make with PHP & jQuery, you will hit a point where that architecture becomes much harder to reason about because you've got state and behavior hooks strewn about between the DOM, database and cache like that guy with the bulletin board conspiracy map meme.