SDIA definition
A digital product or service is what a company or a consumer might buy. It is always made up of software or a combination of software and hardware and, therefore, deals with data, which represents its inputs (by the users), which it transforms into outputs. The quality of a digital product is often measured by how well it does this conversion of inputs to outputs, how those outputs are visualised, how easy it is to input something, how fast it does the conversion, and with what rate of error.
Other definitions
Gartner defines a digital product as follows:
A digital product is a named collection of business capabilities valuable to a defined customer segment. A product may be just software and data. Alternatively, it may comprise any combination of software, hardware, facilities and services, as required to deliver the entire product experience. A product may be a repeatable service (for example, a subscription service); or it may be a platform (one-sided or multisided).