Answer : 4. "IP address"
Explanation :

1. Of all these options, IP addresses are the most important.

2. IP address (Internet Protocol address) is a digital address used to identify a computer or device on the Internet or any other network.

3. IP address is a set of four numbers. It is in this format 191.150.1.38. Is visible in. The set of numbers for an IP address ranges from 0 to 255. That means the IP address ranges from 0.0.0.0 to 255.255.255.255.