What is a 8/16-Bit microcontroller core?

Ambiguation

When checking the datasheets of Microchip:

http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-8493-8-and-32-bit-AVR-XMEGA-Microcontrollers-ATxmega16C4-ATxmega32C4_Datasheet.pdf

, I was confused as the architecture of ATxmega32C4 and ATxmega16C4 is specified 8/16-bit. It should be either 8 or 16 but not both.

Even when searching for ATXMEGA32C3-AUR on a distributer company mouser.com, I see it says

• Product Category: 8-bit Microcontrollers - MCU
• Data Bus Width: 8 bit/16 bit

This makes me even more confuse.

Question

What does 8/16-bit mean in the description of a microcontroller?