A multi-part essay where I try to define of sword and sorcery.
Sword and sorcery has crystallized into a distinctive genre. I don't think its major characteristics are too debatable. That's not to say nuanced distinctions can still be discussed; however, the general outline is established.
First, sword and sorcery is a form of fantasy literature, which means that the virtual reality of the fictional world simulated in sword and sorcery is metaphysically different from our world, the one we experience every day. But how is it different? The major distinction of the sword and sorcery world is the status of the supernatural. Things can happen in sword and sorcery that violate natural laws as we know them. Magic can be worked. The dead can walk. Immortality is a possibility. Though they rarely have an interest in human enterprises, the gods can directly involve themselves in the affairs of mortals.
Aside from this metaphysical distinctiveness, we can also talk about the protagonists and antagonists that anchor sword and sorcery narratives. Sorcerers and monsters show up in sword and sorcery. The protagonists, generally of a non-magical nature, usually fight against them (although some sword and sorcery can have sorcerers as the protagonists).
Some have argued that a distinctive characteristic of sword and sorcery protagonists is that they are much more self-interested than other fantasy protagonists, such as the hobbits and the people of the West in J.R.R. Tolkien's "The Lord of the Rings." I think it's true that sword and sorcery protagonists are not mindlessly altruistic and the scope of their interests is generally local in nature: they are concerned with themselves, their friends, their tribe, their village, etc. I think a fantasy stops being sword and sorcery and starts being more of an "epic fantasy" when the stakes become the world at large.
There are also distinctive settings in sword and sorcery. The majority of them take place in detailed secondary fantasy worlds, worlds that have only a partial connection to our world historically and spatially. Some sword and sorcery can be historical in nature, but in order for fiction with fantasy that takes place in a historical culture to be considered sword and sorcery, you need a supernatural element. The old Sinbad movies are an example. Some might call them sword and sorcery, considering the fantastic elements, despite the fact they are set in a fantasy version of Arabia, an actual culture. I wouldn't call those movies sword and sorcery, but I can imagine an argument that might make that case.
Much more could be said about the kinds of action-based plots that are typical of sword and sorcery; the themes and atmospheres that dominate sword and sorcery narratives, such as the sublime, horror, and unconscious drives, but that will have to wait.