Scalability testing is a form of performance testing aimed at evaluating the capability of a software application or system to scale up or down in response to its demand. This involves testing the software's performance by gradually increasing the load (number of users, transactions, data volume) or changing the infrastructure (adding more CPUs, servers) to observe how it behaves under varying conditions. The goal is to identify the point at which the system's performance starts to degrade, thereby determining its capacity to handle growth in usage. Scalability testing is crucial for ensuring that the application can accommodate future increases in load without compromising on speed, stability, or user experience.