Accumulated amortization is a financial accounting concept that represents the aggregate amount of amortization expense that has been recorded against an intangible asset since it was acquired. Intangible assets are non-physical assets such as patents, licenses, or trademarks, which provide value to a company over their useful lives.

Amortization is the process of allocating the cost of these assets over their useful lifespan, similar to how depreciation is applied to tangible assets. The accumulated amortization figure helps show the net balance or remaining unamortized value of the intangible asset on a company's balance sheet.

For example, if a company acquires a patent for $100,000 and amortizes it over ten years, the annual amortization expense would be $10,000. After three years, the accumulated amortization would be $30,000, and the net book value of the patent would appear as $70,000 on the balance sheet. Understanding accumulated amortization is vital in financial reporting and when analyzing a company's intangible assets.