Answer : 4. "virtual Private Network "
Explanation :

 A Virtual Private Network (VPN) is a technology that allows users to create a secure and encrypted connection to another network over the internet. VPNs are commonly used to ensure privacy and security when browsing the internet, especially when using public Wi-Fi networks. VPNs create a private tunnel for data transmission, protecting users' online activities from surveillance, censorship, and potential cyber threats.