There are different kinds of truncations.

• For example, one can start with `filled' orbits (almost always the lowest), and then allow one, two, three... particles excited out of those filled orbits. These are called 1p-1h, 2p-2h, 3p-3h excitations.
• Alternately, one can state a maximal orbit and allow all possible configurations with particles occupying states up to that maximum. This is called full configuration.
• Finally, for particular use in nuclear physics, there is the energy truncation, also called the \( N\hbar\Omega \) or \( N_{max} \) truncation.