devil's triangle

Short definition from Wiktionary

Noun

1. 1
   An area that is dangerous and where people or vessels may disappear.
2. 2
   A set of three things considered dangerous.
3. 3
   Synonym of devil's threesome.
4. 4
   Synonym of devil's threesome.

Proper noun

1. 1
   An area of the Atlantic Ocean where many ships and planes have disappeared under allegedly mysterious circumstances.
2. 2
   A similar area in the Pacific Ocean.