Commonly used in business, media, and project contexts, just like English 'deadline'.
レポートのデッドラインは明日の午後5時です。
The deadline for the report is tomorrow at 5 p.m.
デッドライン is the casual, business/creative-industry loanword for a deadline, while 締め切り is the standard native Japanese term used in all contexts.
Borrowed from English 'deadline'.