What is meta tag?
The <meta> tag gives metadata about the HTML document.
It is a machine parsable and the metadata will not be displayed on the page.
These elements are typically used to specify page description, keywords, author of the document, last modified, and other metadata.
The metadata can be used by browsers (how to display content or reload page), search engines (keywords), or other web services.

We can use the meta tag as follows:
In short form:

<meta charset="utf-8">

In long form:

<meta http-equiv="Content-Type" content="text/html; charset=utf-8">

Charset Encoding:
It tells the computer how to interpret raw zeroes and ones into real characters.

There are many different types of character encodings, somee of them are ASCII, 8-bit encodings, and Unicode-based encodings.

1. ASCII: It is a 7-bit encoding based on the English alphabet.
2. 8-bit: These encodings are extensions to ASCII that add a potpourri of useful, non-standard characters like and . They can only add 127 characters, so usually only support one script at a time. When you see a page on the web, chances are it's encoded in one of these encodings.
3. Unicode-based: These encodings implement the Unicode standard and include UTF-8, UTF-16 and UTF-32/UCS-4. They go beyond 8-bits and support almost every language in the world. UTF-8 is gaining traction as the dominant international encoding of the web.

List of few meta tags:

1. The title is the first (usually clickable) phrase you see as a search result.

<title>Testing the App </title>

2. A description of your website in 3 of 4 sentences.

<meta name="description" content="text">

3. The keywords under which you wish your website to be found.

<meta name="keywords" content="text">

4. How far do you allow robots to spider through your website.

<meta name="robots" content="selection">

5. How often do you want the spiders to come back and index your website again.

<meta name="revisit-after" content="periode">

6. To define the language in your website.

<meta name='language' content='ES'>

7. To set the author of a page using meta tags.

<meta name='author' content='name, email@gmail.com'>

8. This defines the copyright statements you wish to make about the content on the page.

<meta name="copyright" content="message" />

9. It contains instructions to the browser in the matter of viewports and zooming. In particular, it allows web developers to set the width of the layout viewport.

<meta name="viewport" content="width=device-width, initial-scale=1.0">

10. This information tells about last time the document was updated.

<meta name=revised content=Findnerd, 23/2/2015 />