A horizontal trendline resistance zone is an area on a price chart where price repeatedly fails to move higher, formed by connecting multiple swing highs at similar price levels. This zone represents strong selling pressure, as sellers consistently enter the market near the same level and prevent further upside. Instead of treating resistance as a single line, using a zone accounts for price wicks, volatility, and false breakouts. As long as price stays below this resistance zone, the trend remains weak or range-bound, while a strong close above the zone often signals a potential breakout and start of a new upward move.