"Iperf is a tool for network performance measurement and tuning. It is a cross-platform tool that can produce standardized performance measurements for any network". (Source)

What is Iperf command?
"Iperf is a command-line tool used in diagnosing network speed issues by measuring the maximum network throughput a server can handle. It is particularly useful when experiencing network speed issues, as you can use Iperf to determine which server is unable to reach maximum throughput."

How do I use Iperf on Windows?
"You can download iperf for windows from Iperf For windows. Now unzip this zip file to a folder named "iperf" and run the iperf.exe inside that directory. For example i have extracted, the iperf zip in C:\iperf directory, so will open the Windows CMD, and navigate to that directory, to run the iperf.exe command." (Source)

How does iPerf measure bandwidth?
"Iperf is an open source, free, network performance measurement tool. It works by simply sending traffic from one host to another and measuring the bandwidth that can be achieved. In addition to the throughput measurement it can give metrics such as packet loss, jitter, and traffic distribution."

How to test available network bandwidth using 'iperf'

How do I use Iperf?

Using iPerf to Baseline Network Performance

ESnet Notes - Sample Iperf / Iperf3 Commands