Flashing is the process of writing a new firmware image to the non-volatile memory of a hardware device — replacing whatever was stored there previously. The term comes from flash memory, the type of electrically erasable storage used in most modern microcontrollers. Once flashed, the device executes the new firmware every time it powers on.
The first flash of a new device typically requires a physical USB connection between the device and a host computer. After that, many systems (including ESPHome) support over-the-air (OTA) updates, which deliver new firmware over the network without requiring a physical connection.
In This Home
New ESPHome devices are initially flashed via USB from a workstation. Subsequent firmware updates are pushed OTA through the ESPHome server. See Firmware for more context.