your mother; your home
Polite, formal term used to refer to the listener's mother or home. Extremely rare in modern Japanese; mostly found in classical or highly formal written contexts.
令堂はお元気でいらっしゃいますか。
Is your mother in good health? (very formal, archaic)
令堂にご挨拶申し上げます。
I send my greetings to your home. (very formal, archaic)
The exact derivation is uncertain; the kanji 令 (good, excellent) and 堂 (hall, home) combine to form a respectful term for someone's home or mother.