This is when the lowest energy orbital is filled first

✅ Correct!

The Aufbau Principle (from the German word "Aufbau" meaning "building up") states that in the ground state of an atom, electrons fill atomic orbitals of the lowest available energy levels before occupying higher levels. This principle helps predict the electron configuration of atoms.

For instance, in a hydrogen atom, the 1s orbital has the lowest energy, so it is filled first. Then, electrons move to the 2s orbital, followed by the 2p orbitals, and so on, following the order of increasing energy.