A planet posited in the sign it rules is said to be in its rulership, domicile, or home. Thus, it is able to totally fulfil its role, and it is most likely that its action plays out very positively.
On the contrary, when a planet is in the sign opposite the sign it rules, it is said to be in detriment. Thus, its action is negative, misused, or non-existent or weakened.
A planet in a sign of a similar nature, but which it does not rule, is said to be in exaltation. The planet gets strength and energy from its exaltation, and thus, its influence is positive.
A planet in the sign opposite the sign of its exaltation is said to be in fall. Therefore, contrarily to the exaltation, the planet loses its strength and influence.
When a planet is in none of the enumerated four states, it is in a peregrine state, or it is a peregrine planet.
In two cases out of three, planets are peregrine, and the aspects they form with other planets or angles are even more determining.
This is an important remark that is worth underlining. More and more often, modern astrology decreases the influence of rulerships and pays more attention to aspects.
Statistical observations and practical experiences show that even when a planet is in detriment or in fall, most often, it can play out positively, provided it is well-aspected.
Therefore, caution is to be exercised as you learn those rulership and debility rules that remain nonetheless important.
Here is the rulership list: