What is the Apple laptop charging cable called?

It's a charging cable for the USB-C port.

Apple laptop chargers use a charging cable and charger can be separated from the design, the charger and the cable are separate, when the use is required to connect them together to charge the Apple laptop.

Extended information:

Nowadays, most of the Apple laptops use USB-C port for charging.

The USB-C port is actually a Type-C port, and of course this port normally incorporates the PD fast-charging protocol, which is one of the mainstream fast-charging protocols and is the most popular fast-charging method at the moment. A USB-C port cable adapted with PD fast charging protocol delivers up to 100 watts of power and is free to change the direction of power delivery.

Compared to traditional power cables, USB-C not only has more power and data transmission capabilities, but also has the ability to transmit audio and video, so the Type-C interface will undoubtedly monopolize the consumer electronics transmission interface market now. At present, under the impetus of Google, USB PD has already incorporated Qualcomm's QC fast charging protocol and gained the support of China's Ministry of Industry and Information Technology, so USB-PD is expected to unify the fast charging standard.