It’s BLE - Bluetooth Low Energy.

Basically devices with BLE can listen for a wake-up command and turn on, similar to the “magic packet” of wake on Ethernet.

It also means that most devices with BLE end up flat within a month. I had a speaker with BLE and had to deliberately download a much older version of the Android partner app to turn it off, as they dropped the option to do so in later versions for “convenience”.