I.e. something that doesn't employ separation of concerns / use any form of UI architecture such as MVC, MVP etc.
An example would be a Windows form that had a button which, once pressed (user interaction), grabs data from a database (model), checks it against some business logic and then updates the UI, but all of this written as a single function / all in one class.
One could say badly designed, but I'm sure there is a more appropriate term.
I've come across it termed as Widget-based UI, but this doesn't seem correct.