What is "Download Mode" on the ESP32?

The ESP-WROOM-32E datasheet Table 3 defines that when GPIO0 and GPIO2 are low during startup, you will enter Download mode without Download**mode being defined anywhere in the datasheet:

Download mode is the factory-integrated ROM serial bootloader. By strapping GPIO0 and GPIO2 low at the same time, you can flash a new firmware using the serial port.