It can be installed on both physical server and virtual machines. There licensing policies would differ for physical server and VM's.
To add to @rahul_u comment, take a look at the EULA for ColdFusion 11, particularly section 3.1.2. This will clarify the limitations on what is permitted for installing ColdFusion on a virtual server. Basically, under ColdFusion 11, you can only utilize two virtual CPUs (vCPUs) with a Standard license.