Fibonacci Retracement
Retracement levels 23.6%, 38.2%, 50%, 61.8%, 78.6% used as support/resistance.
Fibonacci retracement is drawn from a swing low to high (or vice versa). Most-watched: 38.2%, 50%, 61.8% (golden ratio). Price often bounces here because everyone watches them. 61.8% is the healthy correction boundary - deeper usually means trend change.
In plain words
After a big move, price rarely goes to zero - it usually pulls back 38%, 50% or 61.8% and stops there. Natural bounce levels.
Example
BTC move 25k->70k. Fib 38.2% = 53k, 50% = 47.5k, 61.8% = 42k. The 2024 correction stopped exactly at 50% (47k).
Also known as: fib retracement, golden ratio