Scalability refers to the ability of a system, network, or application to handle increasing workloads or expand in capacity without compromising performance, stability, or efficiency. In software development, scalability is a critical consideration, especially for applications that anticipate growth in user base, data volume, or transaction rates. A scalable system can accommodate growth by adding resources, such as processing power, memory, or storage, either vertically (increasing the capacity of existing hardware) or horizontally (adding more machines to a system).

Scalability can be measured in terms of performance (how well the system maintains speed and responsiveness under load), capacity (how much workload the system can handle), and cost-efficiency (how economically the system can scale). Achieving scalability often involves careful architectural planning, including the use of load balancers, distributed databases, microservices, and cloud computing platforms that can dynamically allocate resources based on demand. Scalability is essential for businesses that expect to grow, as it ensures that their systems can continue to function smoothly and meet user expectations as demand increases.