An HTML Minifier is an online tool that reduces the size of HTML code by removing unnecessary spaces, line breaks, comments, and other redundant characters. It helps make HTML files smaller, which can improve website loading speed and reduce bandwidth usage. Developers, web designers, and website owners can use an HTML Minifier to optimize their code without changing how a webpage looks or functions. However, it is always a good idea to test the minified code before using it on a live website.