adverb, adverb taking the 'to' particle, noun or participle which takes 'suru'
minutely; in detail; with particular attention
Describes doing something in a detailed, meticulous manner, often with attention to small points. Can be used adverbially or with する to mean 'to go into details'.
彼はその計画について細々と説明した。
He explained the plan in detail.
Let's talk about the details later.