Horizontal and diagonal resistance are both types of trendlines used in technical analysis to identify levels at which an asset's price might face obstacles or reverse direction.

Horizontal resistance refers to a level where the price of an asset has previously encountered significant selling pressure and failed to rise above it. It is a straight, horizontal line drawn across a chart at a price point where the asset has repeatedly reversed or struggled to break through. This type of resistance is often seen in a consolidation phase or at a well-defined price ceiling. Horizontal resistance is considered stronger because it represents a consistent level where market participants consistently sell or exit positions.

Diagonal resistance, on the other hand, is drawn at an angle, often in an uptrend, and represents a level where the price faces resistance as it rises. It is typically drawn by connecting highs over time, forming an upward-sloping line. This type of resistance adjusts for the price’s increasing value over time and is often used to spot the end of a trend or the formation of patterns like rising wedges or triangles.

In summary, horizontal resistance is static, while diagonal resistance is dynamic, adjusting as the price moves over time. Both are essential for identifying potential reversal points.