Greylag goose (Ngỗng xám, Anser anser) is a species of large goose in the waterfowl family Anatidae and the type species of the genus Anser.

Greylag goose or graylag goose 
(Ngỗng trời, Ngỗng xám, Anser anser) 

The greylag goose (Anser anser) is a species of large goose in the waterfowl family Anatidae and the type species of the genus Anser.

The bird's distribution is widespread in Europe and Asia some of which often migrate southwards to spend the winter in warmer places, and many of which are resident, even in the north. 

anas, anatis: Latin duck.
The genus name Anser comes from the Latin word anser meaning "goose".