This is the 4149th most frequent Russian word.
романов
The Russian word "Романов" refers to "Romanov," which is the name of a Russian imperial dynasty.
The word "романов" here is used in the context of literary works, specifically novels.
Я прочитал несколько романов этого автора.
I have read several novels by this author.
The word "Романовых" refers to a family name, specifically the Romanovs, a historical Russian royal family.
Она рассказала мне историю семьи Романовых.
She told me the story of the Romanov family.
"Романовых" in this sentence again refers to the royal family, presented in the possessive case to indicate ownership or relation.