What is Trendline and why trendline is important in trading?

What is Trendline and its importance?
As technical analysis is built on the assumption that prices trend, the use of trend lines is important for both trend identification and confirmation. A trend line is a straight line that connects two or more price points and then extends into the future to act as a line of support or resistance.
Many of the principles applicable to support and resistance levels can be applied to trend lines as well.
Supply and Demand zones are horizontal Support & Resistance whereas trendlines are dynamic Support & Resistance