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The bird genus Apus comprise some of the Old World members of the family Apodidae, commonly known as swifts.
The name Apus is Latin for a swift, thought to be a type of swallow with no feet (from Ancient Greek a meaning "without", and pous meaning "foot").

1/ Little swift (Yến cằm trắng, Apus affinis)

2/ Pacific swift or fork-tailed swift (Yến hông trắng, Apus pacificus)
pacificus refers to the Pacific Ocean.

Cook's swift (Apus cooki)

Cook's swift (Apus cooki) is a small bird in the swift family Apodidae.
Cook's swifts breed in limestone caves of Thailand, Myanmar and Indochina. 

Apodidae, Apus is Latin for a swift, thought to be a type of swallow with no feet (from Ancient Greek a meaning "without", and pous meaning "foot", Greek apous meaning "footless").

House Swift
(Nepal House Swift) 
(Apus nipalensis)

The house swift (Apus nipalensis) is a species of swift in the family Apodidae. 
The bird is found in Japan, Nepal, and Southeast Asia.

The family name, Apodidae, is derived from the Greek apous meaning "footless", a reference to the small, weak legs of these most aerial of birds.
The name Apus is Latin for a swift, thought to be a type of swallow with no feet (from Ancient Greek a meaning "without", and pous meaning "foot").
Nipalensis means from Nepal.

Little swift (Yến cằm trắng, Apus affinis)

The little swift (Apus affinis) is a small species of swift found in Africa and southwestern Asia, and a local breeder in southern Europe.

The name Apus is Latin for a swift, thought to be a type of swallow with no feet (from Ancient Greek a meaning "without", and pous meaning "foot").
The Latin word affinis means "related," "neighboring," "akin to," or "connected," derived from the roots "ad" ("to, toward") and "finis" ("border, end").

Pacific swift or fork-tailed swift 
(Yến hông trắng, Apus pacificus)

The Pacific swift (Apus pacificus) is a species of bird that is part of the Swift family. 
The bird breeds in eastern Asia and is strongly migratory, spending the northern hemisphere's winter in Southeast Asia and Australia.