Support and resistance is one of the most widely used concepts in forex trading.
When the price moves up and then pulls back, the highest point reached before it pulled back is now resistance. Resistance levels indicate where there will be a surplus of sellers. When the price continues up again, the lowest point reached before it started back is now support. Support levels indicate where there will be a surplus of buyers. In this way, resistance and support are continually formed as the price moves up and down over time. The reverse is true during a downtrend.