A matter to be discussed or handled; an item on an agenda.
次の案件に移りましょう。
Let's move on to the next item (on the agenda).
この案件はさらに検討が必要です。
This matter needs further consideration.
その案件は私が担当します。
I'll be responsible for that case/matter.
(Law) a case (e.g., a court case or investigation).
その刑事案件はまだ未解決だ。
That criminal case is still unsolved.
弁護士がその案件を引き受けた。
A lawyer took on that case.
A project or business undertaking (e.g., a contract or job to be carried out).
大型の案件を受注して、チームを増員した。
We won a large contract and increased the team.
この案件は来月から着手する予定です。
This project is scheduled to start next month.
Colloquially, can refer to an advertisement or sponsored spot.
ラジオで新しい案件が流れるらしいよ（＝広告が入る）。
I heard a new ad will run on the radio (i.e., a sponsored spot).
あの企画はスポンサー案件として扱われた。
That program was treated as a sponsor-backed spot.