principal residence; main home
Refers to one's primary home, often in contrast to a secondary residence or villa. Used in formal and legal contexts.
He has a villa in addition to his principal residence.
本宅の住所を教えてください。
Please tell me the address of your main home.
本宅 is one's main, permanent residence, in contrast to 別荘, a secondary home used only occasionally.
Compound of 本 (main) and 宅 (residence). The exact historical derivation is uncertain, but the meaning is transparent from the kanji.