Fibonacci is found throughout trading literature. Fibonacci is mainly found in discussions concerning support and resistance levels. Leonardo Fibonacci was an Italian mathematician who was around during the 12th century and is attributed to discovering the "Fibonacci numbers". These numbers refer to a sequence of numbers where each successive number is the sum of the two previous numbers i.e.1, 2, 3, 5, 8, 13, 21 etc.

Key Fibonacci ratios are 38.2%, 61.8% and 1.618%.

Support and resistance levels are created by drawing a line between two extreme points and then dividing the vertical distance by Fibonacci ratios. Prices are expected to find support or resistance at these price levels.

For more information see the following links:
Wikipedia
http://en.wikipedia.org/wiki/Fibonacci_number

Investopedia
http://www.investopedia.com/terms/f/fibonaccilines.asp
http://www.investopedia.com/terms/f/fibonacciretracement.asp