The show looks inwards, at the darker aspects of humanity and society. This is done through the theme of technology, hence the second meaning. The black mirror is the screen that rules our lives. Taking contemporary phenomena (ranging from the wild popularity of talent shows on TV to the impact of social media and smartphones on our lives) as a starting point and speculate how such phenomena could/would evolve in the future. Each episode tells a different story with different protagonists and focuses on a different theme.
There are three episodes, each a bleak and dark story about how the modern, internet and technology filled world could plunge us into hell. The first, is one set in the present. A fictional princess is kidnapped by an unknown person and a video ransom is posted anonymously on YouTube saying that unless the (fictional) prime minister had sexual intercourse with a pig live broadcast on every British television channel in four days, she would be killed.
The next episode is one about a hopefully-far future, where everything is commercial and false, and everybody is trapped and must play games to make false money to spend on false objects. They feed out of fake food-dispensing machines, which gives out fake, packaged fruit. It is an entirely commercial world, and there appears to be no outside.
It shows two attempts to escape from the drag that life has become, each working, to an extent, before it becomes just as fake and dull as before. The way this is done is by going on an exaggerated, satire of a talent show and winning it. It features a lot of references to how people take the Nintendo Wii and gaming seriously, internet advertising and how wrong it seems and talent contests and how much they are a scam.
The third is a dark 'love' story set in the near-future about how wrong it could be if people could re-watch their memories and show others. People seem to be forced to have small chips implanted behind their ears so their vision is being recorded and can be played back on any screen using a small tool and a super-fast, Wi Fi that is everywhere. It's idea is that people could become obsessed with the past and search their memories for tiny details, eventually causing insanity and a bad ending.
It follows a man who obsesses over the behaviour of his girlfriend at a party the last night and the idea that she is having an affair with a man he clearly hates who was at the party. It psychologically goes through him trying to find out whether she is having an affair or not, and eventually completely losing it and using the memory-viewer, proves that she is. The 'proof' though, is never revealed to be completely genuine.