It's clear that in the game of D&D, 'good' and 'evil' are objective. The 5th edition Player's Handbook gives a few small examples of alignment behaviour on page 122, such as:
Lawful Good (LG) creatures can be counted on to do the right thing as expected by society.
Neutral Evil (NE) is the alignment of those who do whatever they can get away with, without compassion or qualms.
These and other examples in the PHB suggest that helping others or 'following your conscience' are good acts, whereas theft and violence are evil acts. Thus, it seems 'good' is somewhat open to interpretation – it involves having a moral or civil 'conscience'.
Alignment gets another short mention in the chapter on spellcasting, in the sidebar on page 203:
Creating the undead through the use of necromancy spells such as animate dead is not a good act, and only evil casters use such spells frequently.
This is again a little unclear – by describing it as 'not good' it leaves both 'neutral' and 'evil' available, but goes on to say it's only used frequently by evil casters.
My question is, are there any other references, in particular more specific ones, to what constitutes a good or evil act in D&D 5th edition?