What does it mean to "redline sth"?

Question

Thx

Answer 1

I have seen it used in two ways.

1. To put a red line under something written or printed, so that you will notice it again, especially like an appointment in a diary.

2. To drive a piece of machinery harder and harder until the needle on one of its dials reaches the red line that marks the safety limit. One time when I bought a new car, the salesman said, "Don't redline it for the first 2000 miles".

Answer 2

means discriminating some thing