The document discusses the second conditional, also known as the unreal conditional. It is used to talk about unlikely or impossible hypothetical situations. The structure is "if clause" (using past tense verb) + "possible result" (using would/could/might + base verb form). Examples are given such as "If I won the lottery, I would buy a house on a tropical island" and "If I had a superpower, I would teleport." Exceptions for using "were" instead of "was" in the if-clause are also explained.