Which operator allows for flexible matching of multiple criteria in a MongoDB query?

The operator that allows for flexible matching of multiple criteria in MongoDB queries is the $or operator. This operator enables you to specify multiple conditions, and if any of those conditions are satisfied, the document will be included in the result set.

Using $or is beneficial when you want to retrieve documents that match at least one of several different criteria. For example, if you are querying for users who either live in New York or have a role of 'admin', you would use the $or operator to combine these two conditions into one query.

While $and also allows for matching multiple criteria, it requires all specified conditions to be true, making it less flexible than $or in scenarios where any one of the conditions can be sufficient. The $nor operator is used to match documents that do not satisfy any of the specified conditions, which serves a different purpose entirely. The $in operator is used for matching values in an array, which is useful in its own context but does not provide the same level of flexibility for combining multiple distinct criteria as the $or operator does.