Dignity
How well a planet functions in a particular sign - its strength or weakness.
Planetary dignity describes how comfortably a planet operates in a given sign. In domicile, the planet rules the sign and is at home. In exaltation, it's honored and elevated. In detriment (opposite its domicile), it struggles. In fall (opposite its exaltation), it's debilitated. These aren't "good" or "bad" but describe ease of expression. A planet in detriment must work harder but often develops more nuance.
Example
Mars is in domicile in Aries (powerful and direct), but in detriment in Libra (must learn diplomacy over directness).