expression, noun
privacy of correspondence
Legal term referring to the right to have one's letters and other correspondence kept private, protected under constitutional or statutory law.
憲法は信書の秘密を保障している。
The constitution guarantees the privacy of correspondence.
Compound of 信書 (しんしょ, 'letter, correspondence') + の (possessive particle) + 秘密 (ひみつ, 'secret, privacy'). The phrase is a fixed legal expression.