截止 (jié zhǐ) means 'to close, stop, or end by a deadline' — it's used for the action of applications, registrations, etc., reaching their cut-off time. It differs from 截至 (jié zhì), which means 'up to (a specified time)' and is used like a preposition to indicate the point up to which something is valid (e.g., 截至昨天 'as of yesterday'). 结束 (jié shù) is a general 'to end/finish' without the deadline nuance.