When an instance is launched, there has to be a definition of the amount of resources that will be allocated to the instance. In OpenStack, this is defined by what are called flavors. A flavor defines the allocation of virtual CPUs, RAM, and disk space that an instance will use when it launches. When Triple-O installed your system earlier, it created a few flavors for you. Let's take a look at those. Go ahead and source an overcloudrc file. Once you have one sourced, list the flavors, as follows:
undercloud# openstack flavor list
You can create your own flavors if these do not fit your needs exactly, though only the admin user can create new flavors. There is nothing magical about the flavors that Triple-O has created. They have been created close to what the rest of the cloud industry uses for convenience. We are not going to get too deep into flavors; we'll just use the preconfigured flavors that you have just listed.