'Responsive Design' refers to a web design approach that ensures web pages are effectively displayed across a diverse array of devices and screen sizes. This method strives to deliver an optimal viewing experience — characterized by ease of reading and navigation with minimal resizing, panning, and scrolling — on a spectrum of devices, ranging from desktop computer monitors to mobile phones.

First advocated by Ethan Marcotte in 2010, responsive design utilizes fluid grids, flexible images, and media queries. The fluid grid concept advocates for sizing page elements in relative units, such as percentages, instead of fixed units like pixels or points. Similarly, flexible images are set in relative units to avoid extending outside their container elements.

Media queries enable the application of different CSS style rules based on the device's characteristics, particularly the browser width. This approach empowers web developers to craft single web pages that adapt to various screen sizes and orientations, thereby reducing the need for distinct design and development phases for each new device entering the market.

Given the plethora of devices used to access the internet, responsive design has become an indispensable aspect of web development. It plays a vital role in enhancing user experience, boosting accessibility, and fine-tuning web interactions across different devices.

To sum up, responsive design transcends being a mere technical solution; it embodies a philosophy geared towards creating web environments that are accessible and functional for all users, irrespective of their device. In contemporary web development, it is a standard practice crucial for guaranteeing that web content is both accessible and user-friendly on any device.