"Not mounted" - Meaning on a schematic
Neither the bypass capacitor C34 nor the SPI flash chip U3 has been populated on the board (since they're both inside the dashed box). 

The footprints for both are there, and you could add them yourself (look for the designators C34 and U3). Be sure to add the bypass capacitor C34, if it's not already there, should you decide to add the flash chip.