Physical / electrical concepts

Wire-OR (open-drain logic)

The property that any device on an open-drain bus can pull it low without conflict. If two devices try at once, the result is just "low" — no damage.

How it looks

Drawing

Any one chip pulling low wins; nobody fights.

On an open-drain wire, every chip can only pull low or let go; a pull-up does the rest.
If any chip pulls low, the wire is low. If all let go, it is high. Two pulling at once is simply low: no short.
That makes arbitration possible: chips can start talking together and notice who won.

Used by I2C; the unsafe version on push-pull wires is bus contention / collision.