Can someone identify this symbol in the Arduino schematic?

Other Hardware General Electronics
1

Does anyone know what this symbol is?

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2

It is a printed circuit pad that is normally shorted out. You can cut the short and then connect it up again with a blob of solder.

3

Although in this particular case I believe it is used more as a multiple-ground separation technique than a "configurable connection". The designers most likely wanted to keep the USB cable ground somewhat separate from the remaining microcontroller ground (note the ATmega8U2 has separate grounds for this purpose).

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The MegaRAM shield: add 128 kilobytes of external RAM to your Arduino Mega/Mega2560