What is retro in gaming?

Excuse me, could you please clarify what exactly is meant by the term 'retro' in the context of gaming? I've heard it being used quite often, but I'm not entirely sure what it encompasses. Is it simply referring to older games from a bygone era, or does it have a broader meaning that includes certain stylistic elements or gameplay mechanics? I'm curious to learn more about this term and how it's been applied in the gaming industry over time.