fat tail

Short definition from Wiktionary

Noun

1. 1
   A mass of fat stored in the rump of a beast as an adaptation to heat and harsh environmental conditions or selection by man.
2. 2
   The relatively high probability of a relatively extreme outcome.
3. 3
   A tail of a probability distribution with significantly higher kurtosis than a normal distribution (which has kurtosis = 0).
4. 4
   A tail of a probability distribution with infinite variance.
5. 5
   Synonym of fat-tailed sheep.