It is pieces of code that are added to the HTML code of a site in order to improve the visibility and understanding of the content of a page for search engines.
This data enriches the information that is transmitted to the search engines. They will then be able to understand information on your page such as an address, phone number, notices, etc... and display it in search results.
The purpose of Microdata is to make your site more understandable to search engines. This will allow them to offer content that is more adapted and more responsive to the requests of Internet users.
As a result, Microdata has an influence on your positioning because it helps crawlers to index your content and associate it with user requests.
Microdata also allows you to enrich the semantics of the page by specifying data related to content, context, etc. For example, for a blog article, additional data such as author, date, etc. can be found.
By specifying these data, Google will be able to give you access to the "rich snipped" that will make your content even more attractive to the Internet user in the SERP and increase your click-through rate.
To write these tags, there are 3 possible syntaxes: JSON-LD, RDFa and Microdata.
Example of syntax in JSON-LD :
<html>
<head>
<title>Party Coffee Cake</title>
<script type="application/ld+json">
{
"@context": "https://schema.org/",
"@type": "Recipe",
"name": "Party Coffee Cake",
"author": {
"@type": "Person",
"name": "Mary Stone"
},
"datePublished": "2018-03-10",
"description": "This coffee cake is awesome and perfect for parties.",
"prepTime": "PT20M"
}
</script>
</head>
<body>
<h2>Party coffee cake recipe</h2>
<p>
This coffee cake is awesome and perfect for parties.
</p>
</body>
</html>
It is recommended to use tags listed on schema.org, which is the protocol that structures web pages as they are known all over the world. There, you will also find all the indications to set up your Microdata.