[Jtsummers]

You can apply software engineering to develop an application, but you can also do application development without any proper software engineering.

Software Engineering is a design discipline, management discipline, and engineering discipline. Application development is (principally) the act of building an application by writing code. It doesn't require design, management, or engineering discipline to accomplish. But it's better if you've done those things (minimally, the engineering and design portions).

At the same time, a junior software engineer may not be responsible for anything but the writing of code, where others have determined the design and engineering aspects and are conducting project management for them. Or with only limited responsibility (such as developing tests for the aspects they're responsible for developing, which is a part of the engineering discipline: V&V).