Social Insurance Number (SIN) is a unique nine-digit number that the Canadian government issues to all its citizens and residents who are permitted to work and pay taxes in the country. In Canada, there are several synonyms that are used interchangeably for the term Social Insurance Number that includes SIN Card, SIN Number, SIN Card Number, Social Security Number, SSN, and SIN Card Identifier. These terms are used to identify a person uniquely from the other residents and help the Government to administer various programs, including Employment Insurance, Canada Pension Plan, and Old Age Security. The SIN is a crucial piece of information for any Canadian citizen or resident to have as it is a key part of their identity.