Any Information Society service, that is to say, any service normally provided for remuneration, at a distance, by electronic means and at the individual request of a recipient of services.
For the purposes of this definition:

i. “at a distance” means that the service is provided without the parties being simultaneously present;

ii. “by electronic means” means that the service is sent initially and received at its destination by means of electronic equipment for the processing (including digital compression) and storage of data, and
entirely transmitted, conveyed and received by wire, by radio, by optical means or by other
electromagnetic means;

iii. “at the individual request of a recipient of services” means that the service is provided through the
transmission of data on individual request.

Source: Article 1(1)(b) of Directive (EU) 2015/1535, as quoted by NIS2

glossary