Straight Line Basis

A method of computing amortization (depreciation) by dividing the difference between an asset's cost and its expected salvage value by the number of years it is expected to be used.

Investopedia Says:
Also known as straight line depreciation or straight line amortization, this is the simplest deprecation method. Basically, it just spreads out the cost of an asset equally over its lifetime.

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Appreciate the different methods used to describe how book value is "used up". Valuing Depreciation With Straight-Line Or Double-Declining Methods
Companies make choices and assumptions in calculating depreciation, and you need to know how these affect the bottom line. Appreciating Depreciation

Method of depreciating a fixed asset whereby the asset's useful life is divided into the total cost less the estimated salvage value. The procedure is used to arrive at a uniform annual Depreciation expense to be charged against income before figuring income taxes. Thus, if a new machine purchased for $1,200 was estimated to have a useful life of ten years and a salvage value of $200, annual depreciation under the straight-line method would be $100, charged at $100 a year. This is the oldest and simplest method of depreciation and is used by many companies for financial reporting purposes, although faster depreciation of some assets with greater tax benefits in the early years is allowed under the Modified Accelerated Cost Recovery System (MACRS).

Depreciation method whereby an equal amount of the asset's cost is considered an expense for each year of the asset's Useful Life.

Equal annual reductions in the Book Value of property. It is used in accounting for replacement and tax purposes. See Depreciation (Accounting).
Example: A property has a Depreciable Basis of $275,000. For tax purposes, a Useful Life of 271⁄2 years is used with no Salvage Value. Using straight-line depreciation, the book value of the property is decreased by $10,000 ($275,000/27.5) per year. The tax deduction for depreciation is $10,000 per year.

A method employed to calculate the decline in the value of income-producing property for the purposes of federal taxation.

Under this method, the annual depreciation deduction that is used to offset the annual income generated by the property is determined by dividing the cost of the property minus its expected salvage value by the number of years of anticipated useful life.