Definition
Responsive design is an approach to building websites and applications so they automatically adjust their layout to fit any screen size — from a large desktop monitor to a tablet to a mobile phone. Rather than building separate versions for different devices, a responsively designed site uses flexible grids, scalable images, and layout rules that adapt based on the available space. The content stays the same; the presentation changes to suit the device.
Why It Matters
More than half of all web traffic comes from mobile devices. If your website or application does not work well on a phone, you are providing a poor experience to the majority of your visitors. Beyond user experience, search engines like Google use mobile-friendliness as a ranking factor — a site that is not responsive will perform worse in search results. For business applications and portals, responsive design ensures that staff and clients can access the tools they need regardless of which device they are using, without needing a separate mobile app.
Example
An accounting firm launches a client portal where clients can view invoices, download statements, and approve quotes. The portal uses responsive design, so when a client opens it on their laptop they see a full table of invoices with sortable columns. When they open the same URL on their phone, the layout shifts to a card-based view where each invoice is a tappable summary. The data and functionality are identical — only the layout changes to suit the smaller screen.