Writing down allowance
From ACT Wiki
1. UK tax.
The annual tax allowance given to a business in respect of capital allowances for their qualifying capital expenditure.
For example, 18% per year on the reducing balance of unrelieved capital expenditure for many types of assets, from April 2012.
Similar tax relief under other tax systems.
Sometimes known as 'tax depreciation' to distinguish it from accounting depreciation (which is not normally an allowable expense for tax purposes).