The conventional framing of levels as having holding power. Mechanically, a level only holds when the orders currently at it are sufficient to absorb arriving aggression.
Full Explanation
Support and resistance are the most universal concepts in retail trading, and they describe something real — just not what most traders think. A level that held before is not inherently more likely to hold again. What gave it significance was the orders sitting there at that moment. Whether those same orders exist now — whether they have been consumed, withdrawn, or dwarfed by larger aggression — cannot be determined by looking at the chart. The mechanical read replaces "will this level hold?" with "when aggression arrives here, is it being absorbed or relocated?" That question can be answered in real time. The first cannot.