I am totally confused about this function.
Every document I can find on internet says exact the same text. But why do we need azimuth parameter here to find the target coordinate?
Well, 'azimuth' here is actually more the same as 'heading', or 'forward azimuth' to be clearer.
The following pictures can explain the concept quite well I believe.
These terms are commonly used in geo-surveying, distance and angle measurements.