An expression of extreme surprise with strong South-East Asian roots. Best if said with a Singaporean/Malaysian accent. Alternative spellings include "Wah Lau" and "Wa Lau". The infamous Luncaster can often be heard exclaiming "Wallau" for trivial reasons.
1) Wallau! Your mom is so hot!
by Andrew Tong-Goh-Kim October 09, 2006