Basic HTML
<!DOCTYPE>: Defines the document type
<HTML>: Defines an HTML document
<head>: Contains metadata/information for the document
<title>: Defines a title for the document
<body>: Defines the document's body
<h1> to <h6>: Defines HTML headings
<p>: Defines a paragraph
<br>: Inserts a single-line break
<hr>: Defines a thematic change in the content
<!--...-->: Defines a comment
Formatting
<abbr>: Defines an acronym
<abbr>: Defines an abbreviation or an acronym
<address>: Defines contact information for the author/owner of a document/article
<b>: Defines bold text
<bdi>: Isolates a part of the text that might be formatted in a different direction from other text outside it
<bdo>: Overrides the current text direction
<blockquote>: Defines a section that is quoted from another source
<cite>: Defines the title of a work
<code>: Defines a piece of computer code
<del>: Defines text that has been deleted from a document
<dfn>: Specifies a term that is going to be defined within the content
<em>: Defines emphasized text
<i>: Defines a part of text in an alternate voice or mood
<ins>: Defines a text that has been inserted into a document
<kbd>: Defines keyboard input
<mark>: Defines marked/highlighted text
<meter>: Defines a scalar measurement within a known range (a gauge)
<pre>: Defines preformatted text
<progress>: Represents the progress of a task
<q>: Defines a short quotation
<rp>: Defines what to show in browsers that do not support ruby annotations
<rt>: Defines an explanation/pronunciation of characters (for East Asian typography)
<ruby>: Defines a ruby annotation (for East Asian typography)
<s>: Defines text that is no longer correct
<samp>: Defines sample output from a computer program
<small>: Defines smaller text
<strong>: Defines important text
<sub>: Defines subscripted text
<sup>: Defines superscripted text
<template>: Defines a container for content that should be hidden when the page loads
<time>: Defines a specific time (or DateTime)
<u>: Defines some text that is unarticulated and styled differently from normal text
<var>: Defines a variable
<wbr>: Defines a possible line-break
Forms and Input
<form>: Defines an HTML form for user input
<input>: Defines an input control
<textarea>: Defines a multiline input control (text area)
<button>: Defines a clickable button
<select>: Defines a drop-down list
<outgroup>: Defines a group of related options in a drop-down list
<option>: Defines an option in a drop-down list
<label>: Defines a label for an <input> element
<fieldset>: Groups related elements in a form
<legend>: Defines a caption for a <fieldset> element
<datalist>: Specifies a list of pre-defined options for input controls
<output>: Defines the result of a calculation
Frames
<iframe>: Defines an inline frame
Images
<img>: Defines an image
<map>: Defines a client-side image map
<area>: Defines an area inside an image map
<canvas>: Used to draw graphics, on the fly, via scripting (usually JavaScript)
<figcaption>: Defines a caption for a <figure> element
<figure>: Specifies self-contained content
<picture>: Defines a container for multiple image resources
<SVG>: Defines a container for SVG graphics
Audio / Video
<audio>: Defines sound content
<source>: Defines multiple media resources for media elements (<video>, <audio> and <picture>)
<track>: Defines text tracks for media elements (<video> and <audio>)
<video>: Defines a video or movie
Links
<a>: Defines a hyperlink
<link>: Defines the relationship between a document and an external resource (most used to link to style sheets)
<nav>: Defines navigation links
Lists
<menu>: Defines an alternative unordered
<ul>: Defines an unordered list
<ol>: Defines an ordered list
<li>: Defines a list item
<dl>: Defines a description list
<dt>: Defines a term/name in a description list
<dd>: Defines a description of a term/name in a description list
Tables
<table>: Defines a table
<caption>: Defines a table caption
<th>: Defines a header cell in a table
<tr>: Defines a row in a table
<td>: Defines a cell in a table
<thead>: Groups the header content in a table
<tbody>: Groups the body content in a table
<tfoot>: Groups the footer content in a table
<col>: Specifies column properties for each column within a <colgroup> element
<colgroup>: Specifies a group of one or more columns in a table for formatting
Styles and Semantics
<style>: Defines style information for a document
<div>: Defines a section in a document
<span>: Defines a section in a document
<header>: Defines a header for a document or section
<hgroup>: Defines a header and related content
<footer>: Defines a footer for a document or section
<main>: Specifies the main content of a document
<section>: Defines a section in a document
<search>: Defines a search section
<article>: Defines an article
<aside>: Defines content aside from the page content
<details>: Defines additional details that the user can view or hide
<dialog>: Defines a dialog box or window
<summary>: Defines a visible heading for a <details> element
<data>: Adds a machine-readable translation of a given content
Meta Info
<head>: Defines information about the document
<meta>: Defines metadata about an HTML document
<base>: Specifies the base URL/target for all relative URLs in a document
Programming
<script>: Defines a client-side script <noscript>: Defines alternate content for users that do not support client-side scripts <embed>: Defines a container for an external (non-HTML) application <object>: Defines an embedded object <param>: Defines a parameter for an object