What is this symbol on this schematic? (two boxes on wire)
What is this symbol on this schematic? (two boxes on wire)


It is a pair of solder pads, which are joined by default - hence the "wire" (PCB track) between the "boxes" (solder pads).

This is often used as a reversible way to break and join nodes on simple PCBs, which is cheaper than adding a 2-pin header and jumper.

On that schematic, this "solder pad jumper" is used to connect, or disconnect, the USB voltage source (left-hand side of the schematic) from powering the main MCU via the LP38691 regulator.

If you supply a voltage from VIN on the right-hand side of the schematic, you would split (break) that pair of pads, to avoid back-feeding the USB power source, from whatever is providing your VIN, while still allowing you to have a USB data connection.

Look at a photo of the actual PCB which corresponds to that schematic (or read the description of the schematic in its documentation) and you should either see (or read instructions about how to use) that solder pad jumper.



Update: Now that I found the subtle URL in the schematic from the question, I see that schematic is for the Teensy 3.2 (scroll down the linked page, as all schematics are on one page).

Also scrolling down the Teensy pinout page, the reverse of the Teensy 3.2 PCB shows this photo, including the solder pad jumper from the schematic, and instructions of when to cut it (as you found later) in the top-right:



As you can see, the PCB designer chose to use rectangular solder pads for that solder jumper, and this choice has been duplicated in its symbol on the schematic. Other designers use semi-circular pads for this type of jumper on the schematic and/or on the PCB itself.