Hi.
That’s the UUID of the serivce and characteristic of the ESP32 as a BLE device.
Everything is explained on the BLE introduction unit. Module 5, Unit 1: https://rntlab.com/module-5/esp32-bluetooth-low-energy-ble-introduction/

You can also read more here: https://www.bluetooth.com/specifications/gatt/services/

I hope this helps.
Regards,
Sara