Horizontal scalability refers to a system's capability to handle increased workloads by adding more resources or hardware components, enhancing its performance. In contrast to vertical scalability, where performance improvement occurs by adding resources to a single node or machine, horizontal scalability scales by adding additional instances of resources that work together.
Typically, horizontal scalability means the system can distribute loads across multiple machines or servers. Cloud computing platforms are often designed to offer horizontal scalability, allowing resources to be dynamically added or removed as needed to enhance performance and availability.
An example of horizontal scalability is expanding a web server by adding more servers to better handle user requests, rather than just increasing the resources of the existing server.