Responsive Design describes a website or application that adapts to different screens, but the best implementations do more than resize columns.
Navigation may need to change. Content can be reprioritized. Touch targets need more space. Dense data may need a different presentation. The result should feel intentional whether someone is using a phone, tablet, laptop or large monitor.
Design the behavior, not just the breakpoint
A Wireframe is useful because it lets a team decide how information should move and stack before the visual design becomes too expensive to change.