In short
A solid white line at a junction; you must come to a full stop, even if the road is clear.
A stop line is a solid white line across the road, paired with an octagonal 'STOP' sign on approach. Unlike a give-way, a stop line requires a complete stop — even if the road beyond is clear.
A rolling stop at a 'stop' sign is one of the most-marked driving faults on US road tests.
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