This is the 12732nd most frequent Russian word.
красивом
"Красивом" is the prepositional case form of "красивый," meaning "beautiful" in English.
Here, "красивом" is used as a masculine instrumental adjective agreeing with the noun "доме" (house), describing its appearance as beautiful.
Она живёт в красивом доме.
She lives in a beautiful house.
In this example, "красивом" serves as a neuter locative adjective modifying "парке" (park), indicating its characteristic.
Мы гуляли по красивом парке.
We walked in a beautiful park.
Here, "красивом" is functioning as an adjective in prepositional case about the noun "городе" (city), describing it as beautiful.