Triplicity
Triplicity is dignity by element: each of the four elements has rulers who lend a planet moderate support anywhere in that element's three signs.
Where domicile is one sign, triplicity covers three, so it is a broader and gentler support. Most classical schemes give each element a day ruler, a night ruler and a participating ruler, which is one of the places where sect changes the answer.
It sits third on the dignity scale, below domicile and exaltation and above term and face.
Frequently asked
Why does the day or night birth matter here?
Because the triplicity rulers swap: the day ruler of a element takes precedence in a day chart, the night ruler in a night chart.
Is triplicity used in modern astrology?
Less often than domicile and exaltation, but it is standard in traditional practice and our reports compute it.