In finance:
* Social Insurance Number (Canada): A unique nine-digit number assigned to every Canadian citizen and permanent resident for tax and social program purposes.
In technology:
* Secure Internet Network: A private network that is protected by firewalls and other security measures.
* Signal-to-Interference Noise Ratio: A measure of the strength of a signal relative to the noise level.
In other contexts:
* Standard Industrial Number: A code used to classify businesses based on their industry.
* Single In-line Package: A type of electronic packaging that uses a single row of pins.
* System Integration Network: A network of systems that are integrated to work together.
Without more context, it's impossible to determine the specific meaning of SIN. If you can provide more information about where you encountered the abbreviation, I may be able to help you figure out what it stands for.