TripleO can be used in a virtual environment using virtual machines instead of actual baremetal. However, one baremetal machine is still needed to act as the host for the virtual machines.
Virtual deployments with TripleO are for development and testing purposes only. This method cannot be used for production-ready deployments.
The tripleo-quickstart project is used for creating virtual environments for use with TripleO. Please see that documentation at https://docs.openstack.org/tripleo-quickstart/