The One China Policy is the rather tenuous agreement between Taiwan, the Republic of China, and mainland China (the People’s Republic of China) that there is only one China.
The problem is they both claim to be that one China.
That’s made China’s position on the UN Security Council a bit awkward. Taiwan used to be the China on the Security Council but in the seventies, after the Cold War cooled a bit, China took the place as China.
Confused? Yeah, me too. Just watch the episode and you’ll figure it out.