How many VMs can I install on Windows Server 2016 standard?

Standard edition allows you to run two Windows Server VMs and unlimited # of other operating system VMs.

A distinction needs to be made about what the licensing allows; Standard Edition licensing allows for 2 guest Windows OSE instances under a single Standard Edition license for the host.

BUT

You may stack multiple Standard Edition licenses on the host and run as many guest Windows OSE's as your license purchase allows. You could also license your guest Windows OSE's separately if you wanted to. The point is, you're not "limited" to only 2 guest Windows OSE's. The Standard Edition license allows you to license 2 guest Windows OSE's under the hosts license, but you could license and run as many guest Windows OSE's as your hardware supports and your license purchase allows (within the host and guest configuration maximums).