[theamk]

It is hard to define "good" code in general case, but in the specific case of discussing engineer's employment in a specific organization, the answer is pretty simple:

"good" code is the code that you peers consider "good".

That could be because the engineer is writing the code which conforms to all style guides and uses the principles that existing codebase uses; or, in some places, this could be because engineer writes code which performs exceptionally well; or, in other places, this could be because engineer writes code very fast (you probably want to avoid those).