On the line: to be at risk; at risk of failing or being harmed; If something such as your job, career, or reputation is on the line, you may lose or harm it as a result of what you are doing or of the situation you are in; also means speaking on the telephone. As in He wouldn’t put his career on the line to help a friend.
中文释义：面临危险，处于危险之中。一般是put/lay sth on the line，可以是jobs、career、reputation、friendship等等；也可以用put one’s neck/oneself on the line，表示把…置于危险的状态。例句：Almost 3,000 jobs have been lost recently, and a further 3,000 are on the line.（最近已有将近3000人失去了工作，另外还有3000人也面临着失业的危险。) 除此之外，on the line还有打电话、保持通话的意思，这时候line相当于phone。
今日看点：online、on line、on the line你分得清吗?
2.on line = wait in a line of people意思就是排在队伍里。另外，on line有在线、上线的意思，就等于online，大家平时登陆QQ或游戏的上线，就是用online表示。
3.而on the line就和上网、排队没关系了，on the line表示处在危险状态、命悬一线。