Server-side caching stores pre-rendered pages, database query results, and objects on the server. When a user requests a page, the server serves this cached version instead of executing PHP and querying the database, resulting in faster response times. Client-side caching (browser caching) stores static assets like CSS, JavaScript, and images in the user’s browser. This reduces the need to re-download assets on repeat visits, improving load time and decreasing bandwidth usage. Both forms of caching work together to optimize the user experience by reducing server load and speeding up asset delivery.