Responsive breakpoints are a core feature in Swiper.js that let you control how your slider behaves on different screen sizes. When you use breakpoints, you can set specific settings—like how many slides are visible at once or the space between them—based on the width of the user's device. This makes your slider mobile-friendly and ensures it looks great on phones, tablets, and desktops. For example, you might want to show only one slide at a time on a small phone, but display three slides side by side on a large desktop screen. By defining breakpoints in your Swiper configuration, you make sure your slider automatically adapts to any device, providing a smooth and user-friendly experience.