Refers to two persons. Can imply a pair or couple depending on context. The reading ににん is less common and mainly used in formal counting or legal contexts.
The two of us went to see a movie.
あの二人はとても仲がいい。
Those two get along very well.
二人用のテーブルを予約した。
I reserved a table for two.
I watched a movie together with her, just the two of us.
The two of us went on a trip together.
Chloranthus serratus (species of flowering plant)
just the two of them; alone together
Kana spelling; used for clarity, in children's materials, or when the kanji is not needed.
Numerical variant; common in informal writing, lists, or when space is limited.