What does Revelation 16:10 mean?

This bowl judgment is unique in that it's specifically targeted at the "throne" of the beast. The fifth angel's bowl seems primarily to affect the center of the beast's kingdom, the heart of his power. While the other bowl judgments seem to be global, this one might be more localized. That opens up different possibilities for what it might actually be, in literal terms.

This judgment cloaks the beast's kingdom in darkness. The beast and his followers loved moral and spiritual darkness, now they experience a more tangible form of darkness. If this is a literal physical loss of light, it might mean all electrical grids fail, and environmental conditions combine to create a thick, noxious darkness. Without electricity, and in the grip of natural disasters, it would be nearly impossible to use a computer, drive a car, or conduct business. TV news would be silent. Business would fail. Fear will grip people's hearts.

When God smote the ancient Egyptians with darkness, people could not see one another and no one dared to move about (Exodus 10:22–23). The prophet Joel predicted that the tribulation would be a day of thick darkness (Joel 2:2). Afflicted by "harmful and painful sores" (Revelation 16:2) and scorched by the sun (Revelation 16:9), people will not be able to obtain medical help in the total blackout. They will gnaw their tongues in pain. This darkness will preview the horrible outer darkness in which the wicked will spend eternity (see Matthew 8:11–12).