The programming language widely used for server-side web development is JavaScript, specifically through environments like Node.js. This allows developers to build scalable and efficient web applications. JavaScript's versatility enables both client and server-side coding, fostering streamlined development processes. Other notable server-side languages include Python, Ruby, and PHP, each with its strengths and frameworks. JavaScript's popularity makes it a key player in modern web development, facilitating real-time functionalities and engaging user interfaces.