What is the definition of responsive web design?

The definition of responsive web design primarily focuses on its ability to adapt and provide an optimal viewing experience across a wide range of devices. This includes adjusting the layout, images, and functionalities to ensure that users can easily read and navigate the website, whether they are using a mobile phone, tablet, laptop, or desktop computer. The essence of responsive design is flexibility; it allows a single website to be accessible and usable on all devices without the need for separate mobile versions or applications.

The other choices do not accurately reflect the principles of responsive web design. For instance, mobile applications are a different approach altogether and not the core focus of responsive design, which emphasizes a fluid layout rather than being limited to just larger screens. Additionally, the notion of responsive web design being outdated is inaccurate, as it remains a standard and best practice in modern web development. Thus, the ability to work seamlessly across various devices underlines why this answer is the most fitting definition.