Difference between writeoffs and writedowns

All,

I am sorry for asking this basic question. I tried googling it, but I didn’t quite understand what’s on wikipedia. After reading wiki, I believe writedowns are used for impaired assets, and writeoff is a general term used to indicate a reduction in value. However, if this is the case, where there are two different words for the same concept? Can someone please guide me? If there is any self-help type document, I can read it. I am a bit concerned about this because the curriculum uses these two words quite often.

Thanks in advance.

As far as I understand it:

Writedown - simply decrase in value of the item

Writeoff - decrease in value of the item to zero. (Withdrawal from the balance sheet)