Scalability is the feature of a database system that allows it to handle a growing amount of work by adding resources to the system. It is essential for a database to be scalable to accommodate increased data and user load as a company grows. Vertical scaling refers to adding more power (CPU, RAM) to an existing machine, and horizontal scaling means adding more machines to a network to distribute the load. Without scalability, a database system can become slow or unresponsive as demand exceeds its capacity. A database that offers good scalability can grow with the company's needs without requiring a complete overhaul of the system.