Digital reference (more commonly called virtual reference) is a service by which a library reference service is conducted online, and the reference transaction is a computer-mediated communication. It is the remote, computer-mediated delivery of reference information provided by library professionals to users who cannot access or do not want face-to-face communication. Virtual reference service is most often an extension of a library's existing reference service program. The word "reference" in this context refers to the task of providing assistance to library users in finding information, answering questions, and otherwise fulfilling users’ information needs. Reference work often but not always involves using reference works, such as dictionaries, encyclopedias, etc. This form of reference work expands reference services from the physical reference desk to a "virtual" reference desk where the patron could be writing from home, work or a variety of other locations.

The terminology surrounding virtual reference services may involve multiple terms used for the same definition. The preferred term for remotely delivered, computer-mediated reference services is "virtual reference", with the secondary non-preferred term "digital reference" having gone out of use. "Chat reference" is often used interchangeably with virtual reference, although it represents only one aspect of virtual reference. Virtual reference includes the use of both synchronous (i.e., IM, videoconferencing) and asynchronous communication (i.e., texting and email). Here, "synchronous virtual reference" refers to any real-time computer-mediated communication between patron and information professional. Asynchronous virtual reference is all computer-mediated communication that is sent and received at different times.