What is the purpose of the $nor operator in MongoDB?

The $nor operator in MongoDB is specifically designed to combine query clauses with a logical NOR operation. This means that the $nor operator returns documents that do not match any of the specified query conditions. In essence, it filters out documents that meet at least one of the conditions provided within its argument.

When using $nor, you are effectively saying, "give me all documents that do not satisfy any of these conditions," which highlights its role as a negation of the logical OR operation. This is particularly useful when you want to exclude certain documents from your query results based on multiple criteria.

The other options provided reflect different functionalities that do not align with the specific behavior of $nor. For instance, matching at least one query clause would be interpreted as a logical OR operation instead, while filtering documents based on equality pertains to direct comparisons rather than the negation of multiple conditions. Additionally, the option about matching all documents does not accurately represent the operation of $nor, as it is selective and based on the absence of matches to the specified clauses.