A decrease in the value of a company's assets (including intangible assets)
http://en.wikipedia.org/wiki/Depreciation

There's also "Amortization" but I don't think that is as suitable (I'm under the impression amortization is for tangible assets)
"Amortization is generally known as depreciation of intangible assets of a firm."
http://en.wikipedia.org/wiki/Amortization

I know depreciation is usually פחת and I agree that Arthur's answer is a good possibility.
I just found this (in the context of real estate):
Depreciation is a non-cash bookkeeping deduction for estimated wear, tear and obsolescence.
http://articles.chicagotribune.com/2001-02-16/business/01021...

I concede that Arthur's answer may be more accurate, depending on the context, I just wanted to offer this as a potential alternative.

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Note added at 1 hr (2011-11-14 10:33:15 GMT)
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(And hence the medium confidence level)

A suggestion