BSON Types - Database Manual - MongoDB Docs

The $type operator supports using these values to query fields by their BSON type. $type also supports the number alias, which matches the integer, decimal, double, and long BSON types. The $type aggregation operator returns the BSON type of its argument. The $isNumber aggregation operator returns true if its argument is a BSON integer, decimal, double, or long. To determine a field's type, see Ty

[mkusaka]

“Symbol”