A VPN, or virtual private network, allows users to securely connect to another network over the internet. It encrypts data being sent and received to protect it from being accessed by unauthorized parties on public networks. There are different types of VPNs for various uses, such as intranet VPNs that connect corporate offices, extranet VPNs that connect partners/suppliers, and remote access VPNs that allow individual users to securely access a remote network from anywhere. VPNs provide benefits like security, mobility, and reduced communication costs compared to traditional private networks.