Trying to not get to techie about this.
Essentially Responsive Design allows for a web layout – and that includes video files – to adjust to different screen sizes. Meaning the code in the website will know if your website is being consumed on a desktop, tablet, or a smart phone and will adjust it accordingly, so the information can be viewed as optimally as possible.
Responsive design pages use x and y coordinates on a grid for layout and mathematical percentages for images instead of fixed-width parameters. Using percentages instead of fixed-width parameters and a grid layout creates a more fluid layout that will resize itself to fit the size of the display. Got it?