What is a Query?
In databases, queries are requests for specific sets of information. Queries can also be open-ended questions for data that matches your set parameters.
More About Queries
Every WordPress website has a unique database. That database includes all of the content and information stored on your website.
WordPress will query the database to get the information it needs whenever you load a page. Those queries are in SQL, which is the language that databases use.
For any single page, WordPress will likely query the database several times. If a query fails, part of the website might not load. Likewise, if the database takes too long to respond, it can affect your site loading times.
You might run into the occasional WordPress error that says the website can’t connect to the database. That means that queries are not getting a response due to WordPress being unable to access the database.