A retracement is a small reversal in price within a larger price trend. An important word here is "inside.". This distinguishes a reversal from a retracement. Reversals occur when a price trend ends and a new one begins or when a period of consolidation starts. Retracements are merely temporary pauses.
It is clear from examining Forex charts that the market always moves in this general direction. Markets retrace within the majority of trends, and even within very strong trends. Take two steps forward and one step back, or two steps forward and one step back. Bearish and bullish trends both experience retracements. Fibonacci retracements are retracements at Fibonacci levels. The price frequently pauses near Fibonacci levels, which act as both a support and a resistance. It usually happens because traders anticipate it and act accordingly.