One important concept to understand in finance is the useable area of a building. This refers to the total area of a building that can be utilized at any floor level, excluding the space taken up by walls. It is calculated by subtracting the wall area from the plinth area. This term is crucial in determining the efficiency and functionality of a building, and is often used in real estate and property management. Understanding the useable area can help in making informed decisions when it comes to investing in buildings.