HTML elements reference – HTML: HyperText Markup Language | MDN

<acronym>
Allows authors to clearly indicate a sequence of characters that compose an acronym or abbreviation for a word.

<applet>
Embeds a Java applet into the document; this element has been deprecated in favor of <object>.

<bgsound>
Sets up a sound file to play in the background while the page is used; use <audio> instead.

<big>
Renders the enclosed text at a font size one level larger than the surrounding text (medium becomes large, for example). The size is capped at the browser’s maximum permitted font size.

<blink>
Causes the enclosed text to flash slowly.

<center>
Displays its block-level or inline contents centered horizontally within its containing element.

<content>
An obsolete part of the Web Components suite of technologies—was used inside of Shadow DOM as an insertion point, and wasn’t meant to be used in ordinary HTML. It has now been replaced by the <slot> element, which creates a point in the DOM at which a shadow DOM can be inserted.

<dir>
Container for a directory of files and/or folders, potentially with styles and icons applied by the user agent. Do not use this obsolete element; instead, you should use the <ul> element for lists, including lists of files.

<font>
Defines the font size, color and face for its content.

<frame>
Defines a particular area in which another HTML document can be displayed. A frame should be used within a <frameset>.

<frameset>
Used to contain <frame> elements.

<image>
An ancient and poorly supported precursor to the <img> element. It should not be used.

<keygen>
Exists to facilitate generation of key material, and submission of the public key as part of an HTML form. This mechanism is designed for use with Web-based certificate management systems. It is expected that the <keygen> element will be used in an HTML form along with other information needed to construct a certificate request, and that the result of the process will be a signed certificate.

<marquee>
Used to insert a scrolling area of text. You can control what happens when the text reaches the edges of its content area using its attributes.

<menuitem>
Represents a command that a user is able to invoke through a popup menu. This includes context menus, as well as menus that might be attached to a menu button.

<nobr>
Prevents the text it contains from automatically wrapping across multiple lines, potentially resulting in the user having to scroll horizontally to see the entire width of the text.

<noembed>
An obsolete, non-standard way to provide alternative, or “fallback”, content for browsers that do not support the embed element or do not support the type of embedded content an author wishes to use. This element was deprecated in HTML 4.01 and above in favor of placing fallback content between the opening and closing tags of an <object> element.

<noframes>
Provides content to be presented in browsers that don’t support (or have disabled support for) the <frame> element. Although most commonly-used browsers support frames, there are exceptions, including certain special-use browsers including some mobile browsers, as well as text-mode browsers.

<param>
Defines parameters for an <object> element.

<plaintext>
Renders everything following the start tag as raw text, ignoring any following HTML. There is no closing tag, since everything after it is considered raw text.

<rb>
Used to delimit the base text component of a ruby annotation, i.e. the text that is being annotated. One <rb> element should wrap each separate atomic segment of the base text.

<rtc>
Embraces semantic annotations of characters presented in a ruby of <rb> elements used inside of <ruby> element. <rb> elements can have both pronunciation (<rt>) and semantic (<rtc>) annotations.

<shadow>
An obsolete part of the Web Components technology suite that was intended to be used as a shadow DOM insertion point. You might have used it if you have created multiple shadow roots under a shadow host.

<spacer>
Allows insertion of empty spaces on pages. It was devised by Netscape to accomplish the same effect as a single-pixel layout image, which was something web designers used to use to add white spaces to web pages without actually using an image. However, <spacer> is no longer supported by any major browser and the same effects can now be achieved using simple CSS.

<strike>
Places a strikethrough (horizontal line) over text.

<tt>
Creates inline text which is presented using the user agent default monospace font face. This element was created for the purpose of rendering text as it would be displayed on a fixed-width display such as a teletype, text-only screen, or line printer.

<xmp>
Renders text between the start and end tags without interpreting the HTML in between and using a monospaced font. The HTML2 specification recommended that it should be rendered wide enough to allow 80 characters per line.