The RICS Valuation - Professional Standards (the Red Book) defines an intangible asset as:
'A non-monetary asset that manifests itself by its economic properties. It does not have physical substance but grants rights and economic benefits to its owner.'
and goodwill as:
Any future economic benefit arising from a business, an interest in a business or from the use of a group of assets that is not separable.
A number of standard and technical guides are published by various professional bodies that cover intangible assets and goodwill.