This is part of the Building Block category and has matching pieces like columns, tiles, railings and more.
In 2014 the item count (or limit) in all housing was split to have two item counts: one for regular furniture and one for anything in the building block category. See the Housing Item Limit and Building Blocks for details.
The item count varies by the size of the home, but the item count for furniture and all Building Blocks will always be equal. For example, a home that can have 500 furniture items will allow for 500 items in it with the Building Block category tag too, for a total of 1000 placed items.