What term is used to describe a state of relaxation and peace of mind?

The term that describes a state of relaxation and peace of mind is "repose." In a broader context, repose refers not only to physical rest or stillness but also to a mental state of tranquility and ease. This makes it a fitting term for describing a condition where one feels calm and untroubled, away from the stresses of daily life.

Other terms presented do not directly signify a state of relaxation. Juridical possession pertains to the legal acknowledgment of ownership or control over property, emphasizing legal rights rather than personal peace. Demarcation refers to the act of setting boundaries or limits, typically used in surveying or land delineation, which again does not relate to mental or physical relaxation. Allegiance denotes loyalty or commitment to a country or cause, highlighting a sense of duty rather than a state of serene state of mind.