OK, what's the main difference between redundancy and retrenchment?

And say if a company wants to close down a department for non-profit making, would there be any ways a company can escape paying the additional compensation to the laid off workers? Say a worker has been in 15 years in that dept got laid off.

I mean, I read through the act saying that employees can go and claim but I also heard if the employer gives enough notice (like if employees' notice period is 2 months) and they announced 2 months early, they can escape from paying any heavy damages. Is that true?