Refers to the land and buildings of a residence, especially a large or official one. Often used in news reports or formal descriptions.
A burglar broke into the grounds of the residence.
The police searched the premises.
There is a beautiful garden on the grounds.
A fire broke out on the grounds of the estate.
The host gave us a tour of the grounds.
邸宅 means the mansion or residence building itself, while 邸内 means the grounds or premises surrounding it, and the two are easily confused because they share the kanji 邸.
Compound of 邸 (residence) and 内 (inside). The reading ていない is the standard on'yomi combination.