Quantum tomography or quantum state tomography is the process of reconstructing the quantum state (density matrix) for a source of quantum systems by measurements on the systems coming from the source. To be able to uniquely identify the state, the measurements must be tomographically complete, that is the measured operators must form an operator basis on the Hilbert space of the system.

In quantum process tomography on the other hand, known quantum states are used to probe a quantum process to find out how the process can be described.

References

http://research.physics.uiuc.edu/QI/Photonics/Tomography/#what_is_tomography