50 (fifty) is the natural number following 49 and preceding 51.
Fifty is the smallest number that is the sum of two non-zero square numbers in two distinct ways: 50 = 12 + 72 = 52 + 52. It is also the sum of three squares, 50 = 32 + 42 + 52, and the sum of four squares, 50 = 62 + 32 + 22 + 12.
The fifth magic number in nuclear physics.
In Kabbalah, there are 50 Gates of Wisdom (or Understanding)