What does "drm-free" mean?

I'm curious, can you explain to me what the term "drm-free" means? I've seen it used in relation to digital content, like music and books, but I'm not entirely sure what it entails. Is it related to copyright or ownership rights? And what are the benefits of opting for drm-free content over content that's not drm-free? I'd appreciate a clear and concise explanation.