Used before or after a stunt to alert others, relieve pressure, generate more force, and express excitement. It is a sound coming from someone that is in a state of high adrenaline, which is expected during MTB stunts.
There are many functions of YYEEEEWWWW:
- To alarm others
- Clear your mind before a big trick
- Show of and attract attention
- A sense of habit
- Tension control
Although many have chosen to adopt the word YYEEEEWWWW, there are many synonyms including: YEAH, WOO, YEHAW, BRAPPP, *WHISTLE* etc.
(Thanks to Brainy Bikers – Why do Mountain Bikers Say YEW, for the concise definition)