The HTML <aside> element represents a section of the page with content connected tangentially to the rest, which could be considered separate from that content. These sections are often represented as sidebars or inserts. They often contain the definitions on the sidebars, such as definitions from the glossary; there may also be other types of information, such as related advertisements; the biography of the author; web applications; profile information or related links on the blog.
The HTML <base> element specifies the base URL to use for all relative URLs contained within a document. There can be only one <base> element in a document. 
The HTML basefont element (<basefont>) establishes a default font size for a document. Font size then can be varied relative to the base font size using the <font> element.
The HTML Big Element (<big>) makes the text font size one size bigger (for example, from small to medium, or from large to x-large) up to the browser's maximum font size.
The HTML Blink Element (<blink>) is a non-standard element causing the enclosed text to flash slowly.
The HTML <blockquote> Element (or HTML Block Quotation Element) indicates that the enclosed text is an extended quotation. Usually, this is rendered visually by indentation (see Notes for how to change it). A URL for the source of the quotation may be given using the cite attribute, while a text representation of the source can be given using the <cite> element.
The HTML <body> Element represents the content of an HTML document. There can be only one <body> element in a document.
The HTML Center Element (<center>) is a block-level element that can contain paragraphs and other block-level and inline elements. The entire content of this element is centered horizontally within its containing element (typically, the <body>).
The HTML <dd> element (HTML Description Element) indicates the description of a term in a description list (<dl>) element. This element can occur only as a child element of a description list and it must follow a <dt> element.
The HTML Deleted Text Element (<del>) represents a range of text that has been deleted from a document. This element is often (but need not be) rendered with strike-through text.
The HTML Details Element (<details>) is used as a disclosure widget from which the user can retrieve additional information.
The HTML directory element (<dir>) represents a directory, namely a collection of filenames.
The HTML <dl> element (or HTML Description List Element) encloses a list of pairs of terms and descriptions. Common uses for this element are to implement a glossary or to display metadata (a list of key-value pairs).
The HTML <dt> element (or HTML Definition Term Element) identifies a term in a definition list. This element can occur only as a child element of a <dl>. It is usually followed by a <dd> element; however, multiple <dt> elements in a row indicate several terms that are all defined by the immediate next <dd> element.
The HTML <element> element is used to define new custom DOM elements.
The HTML <figcaption> element represents a caption or a legend associated with a figure or an illustration described by the rest of the data of the <figure> element which is its immediate ancestor which means <figcaption> can be the first or last element inside a <figure> block. Also, the HTML Figcaption Element is optional; if not provided, then the parent figure element will have no caption.
The HTML <figure> element represents self-contained content, frequently with a caption (<figcaption>), and is typically referenced as a single unit. While it is related to the main flow, its position is independent of the main flow. Usually this is an image, an illustration, a diagram, a code snippet, or a schema that is referenced in the main text, but that can be moved to another page or to an appendix without affecting the main flow.
The HTML Font Element (<font>) defines the font size, color and face for its content.
<frame> is an HTML element which defines a particular area in which another HTML document can be displayed. A frame should be used within a <frameset>.
<frameset> is an HTML element which is used to contain <frame> elements.