This legacy documentation does not necessarily reflect the current practices in MongoDB driver implementation, but may be useful for historical purposes. See the MongoDB Meta Driver for the current documentation of MongoDB driver implementation.
It is desirable to keep driver interfaces consistent when possible. Of course, idioms vary by language, and when they do adaptation is appropriate. However, when the idiom is the same, keeping the interfaces consistent across drivers is desirable.
In general, use these terms when naming identifiers. Adapt the names to the normal “punctuation” style of your language – foo_bar in C might be fooBar in Java.