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The family Ardeidae, with 72 recognized species, are referred to as egrets or bitterns or herons in the order Pelecaniformes.
Although herons resemble birds in some other families, such as the storks, ibises, spoonbills, and cranes, they differ from these in flying with their necks retracted, not outstretched.

Ardeidae, Ardea: the Latin word ardea meaning "heron".

Les ardéidés, ou Ardeidae, sont une famille d'oiseaux comportant 19 genres et 67 espèces de hérons, aigrettes, butors et apparentés (crabiers, bihoreaux, savacou, onorés et blongios).

Pelecaniformes, Pelecanus: mot grec pelekan, pelekanos pélican.
Ardeidae, Ardea: mot latin qui signifie "hérons".

This is a list of bird species in Vietnam by order.

The Pelecaniformes are an order of medium-sized and large waterbirds found worldwide.
The pelicans, shoebill and hamerkop form a clade within the order, with their next closest relatives being a clade containing the herons, ibises and spoonbills. 

Pelecaniformes    
  Threskiornithidae – ibises, spoonbills (36 species)
  Ardeidae – herons, bitterns (72 species)
  Balaenicipitidae – shoebill
  Scopidae – hamerkop
  Pelecanidae – pelicans (8 species)

L'ordre des Pelecaniformes regroupe des oiseaux palmipèdes et échassiers. 

Pelecanus: mot grec pelekan, pelekanos pélican.

The family Threskiornithidae, which belongs to the bird order Pelecaniformes, includes 36 species of large wading birds. 

Pelecanus: Greek pelekan, pelekanos pelican.

Threskiornis Greek threskeia religious worship (threskeuo to worship); ornis bird. 
The Sacred Ibis Threskiornis aethiopicus was venerated by the ancient Egyptians for its crescent-shaped bill and bright white plumage. They considered it to represent Thoth the moon god.