The Fibonacci sequence is a series of numbers where each number is the sum of the two preceding numbers, starting with 0 and 1. Leonardo Fibonacci introduced this sequence to Europe after learning it from Arab mathematicians during his travels with his merchant father. The sequence is defined by the rule Fn=Fn-1+Fn-2, with terms numbered from 0 and the next terms found by adding the two numbers before it, creating the sequence 0, 1, 1, 2, 3, 5, 8, etc. When plotted geometrically by making squares with widths of successive Fibonacci numbers, the squares form a spiral shape.