What is the origin of the idiom "give someone the pink slip" and when to use it?

The origin of the idiom "give someone the pink slip" is unclear, but it is thought to have originated in the United States in the early 20th century and is believed to refer to the practice of using a pink slip of paper to notify someone of their termination from a job. This idiom is used to describe a situation where someone is fired or dismissed from their job.