"is when two Planets are in each others dignities, as the Sun in Aries, and Mars in Leo, here is a Reception by House, it may be also by Exaltation, Triplicity, Term and Face." [PA
Planets in each other's dignities act as though in good aspect to each other. When in each other's debilities, planets act as though in adverse aspect to each other. Especially important when comparing nativities of two people.
In astrology, reception is a condition where one planet is located in a sign where a second planet has astrological dignity--for example, a sign which the second planet rules or in which it is exalted, or where the second planet is the triplicity ruler.