The tax authorities need to know if the owner of the place is the user, or, on the contrary, if he rents the premises to a third party. In the first case, he will collect the housing tax (TH), badly named.
"A second home is accommodation used for short-term stays (weekends, leisure or holidays)," according to the INSEE definition. It would be more appropriate to speak of a "housing tax" for these dwellings, most often pavilions, "shutters...