What are “Queries”?

Im not sure if this is the correct forum for this as I am not entirely sure what it is as that is the question im asking (hope that makes sense, lol).. Anyways..
When visiting websites, some of them give you information on how many Queries happened when you visited, for example, something like this: "Queries: 26 queries".. What does this mean? and What are "Queries"?

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