The <option> element is used in conjunction with the <select> element to create a drop-down menu in a web form. Each <option> element is displayed as an available option in the resulting drop-down menu.
The <multicol> element was an experimental feature, now deprecated, that was used to create a newspaper-style layout for text content. The modern CSS columns property can be used to create the same effect.
The <p> element is used to identify blocks of paragraph text. The closing <p> tag is optional and is implied by the opening tag of the next HTML element encountered in an HTML document after an opening <p> tag.
The <listing> element was intended as a way to render HTML code on a page. It was never properly supported, and is now deprecated. Using <listing> will almost certainly result in unexpected results. Instead, use <code>, or place the content in a <div> with the appropriate CSS styling.