...
A block of storage that may be attached and detached from VMs similar to a USB drive. These may only be attached to one VM at a time.
Cluster
A group of resources (Nova instances, Neutron networks, security groups etc) combined to function as one system.
Key Pair
A combination of a public key used to encrypt data and a private key used to decrypt data. Typically used in the context of using SSH to connect to a remote machine.
...