Semantic HTML

Definitions

<s>: The <s> tag is used to indicate that the text is no longer accurate or relevant. As you can see in ~~this example~~ here.
<samp>: The <samp> tag is used to define sample output from a computer program. For example, Sample Text.
<script>: The <script> tag is used to define a client-side script (JavaScript).

document.write("Hello World!")
<section>: The <section> tag is used to define sections in a document, such as chapters, headers, footers, or any other sections of the document.
<select>: The <select> tag is used to create a drop-down list.
<small>: The <small> tag is used to define smaller text.

Small Text
<source>: The <source> tag is used to specify multiple media resources for media elements (<video> and <audio>).
<span>: The <span> tag is used to group inline-elements in a document.

This is a red text.
<strong>: The <strong> tag is used to define important text.

Important Text
<sub>: The <sub> tag is used to define subscripted text.

H₂O
<summary>: The <summary> tag is used to define a visible heading for a <details> element.

Click to see the details

<detail> and <summary> can be used to create a nested menu structure, or an accordion control.
<sup>: The <sup> tag is used to define superscripted text.

E = mc²
<svg>: The <svg> tag is used to define a container for SVG graphics.