The drab swiftlet was described by the English zoologist George Robert Gray in 1866 under the binomial name Collocalia neglecta.

[1][2] The specific epithet neglecta is from the Latin neglectus meaning "ignored", "overlooked" or "neglected".

[4][5] There are two subspecies:[5] The drab swiftlet is 9–10 cm (3.5–3.9 in) in length with a square tail.

[7] It has a satin grayish-blue back with slightly glossy crown and tail.

The lower breast, flanks and belly are white but the rump is dark.