Bondout usually means that the internal MCU bus is available for external circuitry, usually an emulator.
This bus allows to simulate internal code memory as well as additional SFR's by using a derivative chip on that bus (dead 51 core for emulated device's special abilities, such as hardware I2C etc.)

You cannot buy such bondout versions or derivatives unless you're an emulator manufacturer.

the bare chip without case is called die.

Cheers, Roger