A cursor in MongoDB with the PyMongo driver refers to the MongoDB cursor object. This cursor is used to iterate through the query results from MongoDB. In PyMongo, the MongoDB cursor is encapsulated by a Cursor object which provides access to methods for iterating and manipulating the query results. The cursor size refers to the maximum number of documents that can be returned in a single MongoDB query. Depending on the particular PyMongo driver you are using, the value of the cursor size can vary. Some PyMongo drivers use a default cursor size of 20, while others might use a different value. Additionally, you can also set a custom cursor size value when creating a cursor query in PyMongo. This value is set using the limit() method which takes an integer argument that sets the maximum number of documents that can be retrieved. Setting a large cursor size value can be helpful in order to reduce the amount of time needed to send multiple queries and retrieve data from the database.