An adverb meaning 'since then' or 'after that', referring to the time following a particular event or point.
あれから彼とは連絡をとっていない。
I haven't been in contact with him since then.
事故の処理は難航したが、あれから状況は安定した。
The handling of the accident was difficult, but the situation has stabilized since then.
大学の卒業式で会って、あれからもう十年になる。
We met at the university graduation ceremony, and it's been ten years since then.