Both ‘advanced agent’ and ‘good’ should be understood as metasyntactic placeholders for complicated ideas still under debate. The term ‘alignment’ is intended to convey the idea of pointing an AI in a direction—just like, once you build a rocket, it has to be pointed in a particular direction.
“AI alignment theory” is meant as an overarching term to cover the whole research field associated with this problem, including, e.g., the much-debated attempt to estimate how rapidly an AI might gain in capability once it goes over various particular thresholds.
Other terms that have been used to describe this research problem include “robust and beneficial AI” and “Friendly AI”. The term “value alignment problem” was coined by Stuart Russell to refer to the primary subproblem of aligning AI preferences with (potentially idealized) human preferences.
https://arbital.com/p/ai_alignment/