Final answer:
The JDBC Type 4 driver is known as the thin driver because it's a pure Java implementation that doesn't need native code on the client and directly translates JDBC calls into the network protocol used by the DBMS.
Step-by-step explanation:
The driver often referred to as the thin driver in JDBC is the Type 4 driver. Unlike other JDBC driver types that may require additional binary or native code on the client side, the Type 4 driver is a pure Java implementation that converts JDBC calls directly into the network protocol used by DBMSs, hence it is considered thin. This aspect allows it to be platform-independent and to provide better performance since there's no need to translate the requests from one form to another.