기한(gi-han, gihan)
The final time or period by which something must be completed or submitted
When to use
completion date, legal/official submission time, contract period, assignment submission deadline
The nuance
기한 indicates the deadline or time limit by which something must be done, commonly used in expressions like 'there is a deadline' or 'to meet the deadline'.
마감(ma-gam, magam)
The moment or state when a task or work ends, or the act of closing/completing that task
When to use
work ending time, publication manuscript deadline, sales closing, event registration closing
The nuance
마감 emphasizes the act or point of finishing or closing work, used in phrases like 'closing time arrives' or 'to close/finish something'.