A chain letter is a message that encourages the recipient to send copies to multiple people. Typically, these letters promise good luck, financial gain, or other rewards if the chain is followed. However, they often threaten negative consequences for those who do not participate, creating a sense of urgency. Chain letters can be found in various formats, including physical letters, emails, and social media posts. While some may seem harmless, they can lead to spam and unwanted communication. Additionally, many chain letters are considered a form of pyramid scheme, which is illegal in many jurisdictions.