Pink slip is an interesting term and I tried to research where it came from. I had thought maybe layoff notifications in the days of paper were pink, but it appears that there isn't a definitive answer as to the origin of the term, other than it's been used as long as anyone can remember.
Getting a layoff notice is colorfully described in other countries, too. According to Snopes, in Germany, it's a blue letter and the French military sent a yellow paper.
Synonyms: lay-off notice, termination notice
Read More: How to Handle a Termination