expression, noun which may take the genitive case particle 'no'
one by one; individually; each one
Emphasizes handling or considering items separately, one at a time. Often used adverbially with に or as a pre-noun modifier with の.
See also: 一つ一つ (ひとつひとつ)
りんごを一個一個丁寧に箱に詰めた。
I carefully packed the apples into the box one by one.
一個一個の部品をチェックしてください。
Please check each individual part.