Page speed refers to how fast your site loads for a user, something Google takes into account while ranking websites since a faster loading page directly translate to better user experience. If the interviewer asks what you would do to increase page speed, describe how you’ve achieved this in the past with examples such as reducing image sizes, enabling compression, reducing redirects, removing render-blocking JavaScript, leveraging browser caching, improve server response time, using a content distribution network to compress files, optimizing the code, etc.