Meta tags in HTML documents provide useful information about the document including a description, keywords, author, dates of modifications, and around 90 other fields. This topic covers the usage and purpose of these tags.
Meta tags help in SEO and increase the Ranking of the webpage.

<meta name="description" content="Page Description">

Page Information

application-name:
Giving the name of the Web application that the page represents.

<meta name="application-name" content="TDBEditorPro">

If it’s not a Web application, the application-name meta tag must not be used.

author:
Set the author of the page:

<meta name="author" content="The Pro Developer">

Only one name can be given.

description:
Set the description of the page:

<meta name="description" content="Page Description">

The description meta-tag can be used by various search engines while indexing your web page for searching purpose. Usually, the description contained within the meta tag is the short summary that shows up under the page/website's main title in the search engine results. Google usually uses only the first 20-25 words of your description.

keywords:
Set keywords for search engines (comma-separated):

<meta name="keywords" content="Keyword1, Keyword2">

The keywords meta tag is sometimes used by search engines to know the search query which is relevant to your web page.
As a rule of thumb, it is probably a good idea to not add too many words, as most search engines that use this meta tag for indexing will only index the first ~20 words. Make sure that you put the most important keywords first.

Character Encoding

The charset attribute specifies the character encoding for the HTML document and needs to be a valid character encoding (examples include windows-1252, ISO-8859-2, Shift_JIS, and UTF-8). UTF-8 (Unicode) is the most widely used and should be used for any new project.

<meta charset="UTF-8">

<meta charset="ISO-8859-1">

All browsers have always recognized the <meta charset> form, but if you for some reason need your page to be valid HTML 4.01, you can use the following instead:

<meta http-equiv="content-type" content="text/html; charset=UTF-8">

<meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">

See also the Encoding Standard, to view all available character encoding labels that browsers recognize.

Robots

The robots attribute, supported by several major search engines, controls whether search engine spiders are allowed to index a page or not and whether they should follow links from a page or not.

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

This example instructs all search engines do not to show the page in search results. Other allowed values are:

Note: Explicitly defining index and/or follow, while valid values, is not necessary as pretty much all search engines will assume they are allowed to do so if not explicitly prevented from doing so. Similar to how the robots.txt file operates, search engines generally only look for things they are not allowed to do. Only stating things a search engine isn't allowed to do also prevents accidentally stating opposites (such as index, ..., noindex) which not all search engines will treat in the same way.

Social Media

Open Graph is a standard for metadata that extends the normal information contained within a site's head markup. This enables websites such as Facebook to display deeper and richer information about a website in a structured format. This information is then automatically displayed when users share links to websites containing OG metadata on Facebook.

Facebook / Open Graph

<meta property="fb:app_id" content="123456789">

<meta property="og:url" content="https://blog.theprodevelopers.com">

<meta property="og:type" content="website">

<meta property="og:title" content="The Pro Developer">

<meta property="og:image" content="https://blog.theprodevelopers.com/img/logos/logo.png">

<meta property="og:description" content="We are a full stack team for any of your full-stack web projects ......">

<meta property="og:site_name" content="The Pro Developer">

<meta property="og:locale" content="en_US">

<meta property="article:author" content="@TheProDeveloper">

Facebook / Instant Articles

<meta charset="utf-8">

<meta property="op:markup_version" content="v1.0">

<!-- The URL of the web version of your article -->

<link rel="canonical" href="http://example.com/article.html">

<!-- The style to be used for this article -->

<meta property="fb:article_style" content="myarticlestyle">

Twitter uses its own markup for metadata. This metadata is used as information to control how tweets are displayed when they contain a link to the site.

Twitter

<meta name="twitter:card" content="summary">

<meta name="twitter:site" content="@site_account">

<meta name="twitter:creator" content="@individual_account">

<meta name="twitter:url" content="https://example.com/page.html">

<meta name="twitter:title" content="Content Title">

<meta name="twitter:description" content="Content description less than 200 characters">

<meta name="twitter:image" content="https://example.com/image.jpg">

 

Google+ / Schema.org

<link href="https://plus.google.com/+YourPage" rel="publisher">

<meta itemprop="name" content="Content Title">

<meta itemprop="description" content="Content description less than 200 characters">

<meta itemprop="image" content="https://example.com/image.jpg">

Mobile Layout Control

Common mobile-optimized sites use the <meta name="viewport"> tag like this:

<meta name="viewport" content="width=device-width, initial-scale=1">Project

The viewport element gives the browser instructions on how to control the page's dimensions and scaling based on the device you are using.

In the above example, content="width=device-width means that the browser will render the width of the page at the width of its own screen. So if that screen is 480px wide, the browser window will be 480px wide. initialscale=1 depicts that the initial zoom (which is 1 in this case, means it does not zoom).

Below are the attributes this tag supports:

Notes:
1 The width property can be either specified in pixels (width=600) or by device-width (width=device-width) which represents the physical width of the device's screen.

2 Similarly, the height property can be either specified in pixels (height=600) or by device-height (height=device-height) which represents the physical height of the device's screen.

Automatic Refresh

To refresh the page every five seconds, add this meta element in the head element:

<meta http-equiv="refresh" content="5">

CAUTION! While this is a valid command, it is recommended that you do not use it because of its negative effects on user experience. Refreshing the page too often can cause it to become unresponsive, and often scrolls to the top of the page. If some information on the page needs to be updated continuously, there are much better ways to do that by only refreshing a portion of a page

Phone Number Recognition

Mobile platforms like iOS automatically recognize phone numbers and turn them into tel: links. While the feature is very practical, the system sometimes detects ISBN codes and other numbers as telephone numbers.
For mobile Safari and some other WebKit-based mobile browsers to turn off automatic phone number recognition and formatting, you need this meta tag:

<meta name="format-detection" content="telephone=no">

Automatic redirect

Sometimes your webpage needs an automatic redirect.

For example, to redirect to example.com after 5 seconds:

<meta http-equiv="refresh" content="5;url=https://www.example.com/" />

This is line will send you to the designated website (in this case example.com after 5 seconds

If you need to change the time delay before a redirect, simply changing the number right before your;url= will alter the time delay

Web App

You can set up your web app or website to have an application shortcut icon added to a device's home screen, and have the app launch in full-screen "app mode" using Chrome for Android’s "Add to Home screen" menu item.

Below meta tag(s) will open the web app in full-screen mode (without address bar).

Android Chrome

<meta name="mobile-web-app-capable" content="yes">

IOS

<meta name="apple-mobile-web-app-capable" content="yes">

Do you Know: You can also set color for status bar and address bar in the meta tag.

Android Chrome

<meta name="theme-color" content="black">

IOS

<meta name="apple-mobile-web-app-status-bar-style"