What does the term 'upsert' signify in MongoDB?

The term 'upsert' in MongoDB represents a combination of "update" and "insert." When performing an upsert operation, the database checks to see if a document matching the specified criteria already exists. If it does, MongoDB will update that document with the new values provided in the operation. If it does not find any document that matches the criteria, it will insert a new document with the specified values.

This behavior is particularly useful in scenarios where you want to ensure that a document is either updated with new information or created if it doesn't already exist, allowing developers to write more efficient and concise code without needing to perform separate queries for checking the existence of documents. Thus, recognizing upserts as being about updating existing data or inserting new data enhances the functional understanding of MongoDB's capabilities in handling data operations.