DRC error that a trace touches two different nets. Critical. The autorouter sometimes does this when packed tightly.
How it looks
Illustration on real CORE3588 geometry: the fault is drawn in on purpose. The real board has none.
The Q1 corner of CORE3588 with a short drawn in on purpose. The real board has 0 shorts.
1A drawn-in sliver (white) joining Net-(Q1-B) (amber) to Q1 pin 2, which is ground. DRC would report shorting_items: two nets touching. Here the transistor could never switch on, so the RECORDING light would stay dark.
How it works
Where it fits
A short is worse than a missing join (unconnected_items): it can kill the board when power meets ground.
DRC also catches the near-miss, a gap smaller than the clearance from the capability table, before it becomes a short in the factory.