Dear Roman:
Good day!
Definitive estimates are very narrow estimates. How narrow? There is no hard and fast rule for that. The PMBOK4 mentions ROM estimates from -50% to +50% and narrow estimates from -10% to +10%. Please note that the PMBOK4 doesn’t mentions the term “definitive estimates” anywhere in the guide. However, the PMBOK5 guide does mention the term “definitive estimates” and ranges it from -5% to +10%.
I would not expect such a specific question appearing on the real exam. But if it does, -5% to +10% is your answer.
Warm regards,
Khurram