This is a business tax concept. Business property is considered to lose value at a fixed rate over a set time. For instance, furniture will fully depreciate over 5 years, so you can deduct 20% of its value as an asset loss each year. Large industrial equipment might have a 20 year life, so you can only deduct 5% of the value each year. Depreciation does not reflect "a real" loss of value, but is a way to account for it in a uniform way for everyone. "Accelerated depreciation" is when the tax law allows you to deduct the value over a shorter time, giving you a bigger tax break. This is usually the result of special laws, such as allowing accelerated depreciation for solar panels to make them more attractive to buy.