Support is a price level where a falling price has historically tended to find buying interest and stop declining. Resistance is a price level where a rising price has historically tended to find selling interest and stop rising. Both are best treated as approximate zones, not exact price points, and a broken support level can later act as resistance, and vice versa.
Related Reading
See a full explanation with a visual diagram in How to Read Charts on TradingView: Candles, Indicators, Drawing Tools.