What It Means
A key support or resistance level is a price zone where a stock has repeatedly stopped falling (support) or stopped rising (resistance) in the past, watched closely by traders for a possible reaction if price approaches it again.
How It Works
Support and resistance aren't exact lines — they're zones, because the same "level" rarely gets tested at the identical price twice. A level gets more significant the more times price has reacted at it and the more volume traded there, since that reflects real buying or selling interest clustered at that price. When a resistance level does finally break with strong volume, it often flips and becomes support going forward — the same zone, but now acting as a floor instead of a ceiling.
Warning
Treating support and resistance as precise, unbreakable prices — rather than zones — leads traders to place stop-losses right at the level, where they're the first ones stopped out on a brief wick through it before price reverses as expected.