What type of layout does Bootstrap use for a responsive design?

Bootstrap employs a grid layout for its responsive design, which is a core feature of the framework. The grid system is based on a 12-column layout that enables developers to create responsive web pages that adjust seamlessly across various screen sizes and devices. This structure allows for easy organization and alignment of content, making it straightforward to design layouts that are both visually appealing and functional on desktops, tablets, and mobile phones.

By using predefined classes, developers can specify how many columns an element should occupy on different viewport sizes, providing flexibility in arranging content dynamically. As the viewport size changes, Bootstrap's grid system responds by adjusting the layout without manual intervention, ensuring a consistent user experience across devices.

This method of responsive design contrasts with fluid layouts, which resize fluidly but can lead to unpredictable alignment, and fixed layouts, which maintain a specific width and do not adjust to different screen sizes, potentially resulting in usability issues on smaller devices. Adaptive layouts are generally pre-defined for specific screen sizes and do not utilize the flexible, responsive nature that the grid layout in Bootstrap provides.