Goodwill is an intangible asset, but it doesn't get amortized like other intangible assets (such as intellectual property, patents, copyrights, trademarks, and brand recognition). Instead of getting amortized, Goodwill is tested for impairment yearly.
Goodwill is a plug variable that represents the difference between the book value of the company and the equity purchase price paid for the company. It's also known as the "excess purchase price."