Typically, items used in the day-to-day business of producing income are called "assets". A business asset is anything that is used on a recurring basis to produce income. For a furnished rental property, the furniture would be considered a business asset.

Assets are entered in the assets/depreciation section and get depreciated over time. Furniture is typically depreciated over 7 years. However, there is an exception for items that cost less than $2,500, referred to as safe harbor di-minimus. With this election you can just expense the cost in the year of purchase, if the item cost less than $2,500. Personally, I like this better for low cost items. Otherwise if you depreciate it, then when the day comes (and it will come) that the item needs to be replaced for any reason, then it's disposition has to be accounted for in the assets/depreciation section. The additional work is just not worth it to me.

Besides, if you start depreciating furniture, it can tend to make your list of business assets rather large and more work to deal with as stuff gets broken, wears out, or needs to be replaced for any other reason. Not to meantion the mathimatical headache of dealing with that large list of assets when you sell the property in the future.