What defines a Virtual Private Network (VPN)?

A Virtual Private Network (VPN) is fundamentally defined as a network that is constructed using public infrastructure, like the internet, to provide secure connections between remote users or sites. This setup allows data to be transmitted securely across these public channels by employing encryption and other security measures, effectively creating a private network environment.

Using public wires while ensuring privacy and security is a necessary aspect of a VPN, enabling organizations to maintain connectivity across diverse geographic locations without compromising on data integrity or confidentiality. The VPN achieves this by creating a secure "tunnel" for data transport, which is crucial for individuals or organizations needing safe communication without relying entirely on private lines.

The other provided options refer to different networking contexts or security measures that do not encapsulate the VPN's core functionality of using public infrastructure for secure communication among users and locations.