It is a knowledge base that Google obtains from various sources that it considers authorized.

In general, it is information related to:

• People: We don't necessarily talk about celebrities, it is referring to individuals who have enough information gathered and who are related to others.
• Events: If we look for an event we will also find related results. 
• Places: If we look Barcelona, Knowledge Graph will return us related information: historical data, meteorology, population...

The most interesting thing is that this database is not a simple collection of indexed content associated with a keyword that is displayed in a search. t is able to establish the link between entities that could apparently not have a direct relationship.

Is a knowledge base that has been created by Google with the intention of improving the user's search experience.

Its main objective is to make the search results more human and thus give an exact answer to what the user seeks and wants to know.

The results thrown by Google Knowledge Graph do not depend on keywords but on the context in which the search is made, making associations established in networks that are optimized from the search experience of thousands of users.

The results, in addition, are influenced by your previous behavior, since it takes into account your search history and visits, with the intention of giving just what you are looking for. Google Knowledge Graph includes in your results all the information that you consider relevant for your search and that which is related, therefore you will find recent news, related events and more.

Search is changing — and it’s changing faster than ever. Increasingly, we are seeing organic elements in search results being displaced by displays coming from the Knowledge Graph.

The Knowledge Graph was built to help with that mission. It contains information about entities and their relationships to one another — meaning that Google is increasingly able to recognize a search query as a distinct entity rather than just a string of keywords. As we shift further away from keyword-based search and more towards entity-based search, internal data quality is becoming more imperative.

In other words, if you want to be findable in the search results of the future, search engines need to be able to understand what entities are on your web page.

Search engine technology can extract entity information from your content in two ways — explicitly (using structured data markup), or implicitly (using natural language).

Google started to allow official site representatives to edit/suggest changes to their Knowledge Graph panels.

This is a great feature, as it allows site owners to remove any incorrect information, as well as have the opportunity to update the content on an ongoing basis.

Also, some sites, companies, persons and places only have partial Knowledge Graphs. Some information may not be displaying due to lack of sources or no Wikipedia page. 

So outside of being able to edit your Knowledge Graph result directly, the second option is to optimize the sources that power the Knowledge Graph result, to have accurate and more information appear in the panel.