Answer by Vaibhavi Dhote:
FSI stands for Floor Space index.
The number basically defines the maximum Floor space area you can build on your land with respect to the plot area that you have.
(FSI) x (plot area) = Maximum build-able Floor Space
For Example if you have a plot of land of 100 sq mt and the FSI of that area is 1 then you can build a 1×100 sq mt of floor space. Say if i build 40 sq mt on the ground floor, 40 sq mt on the first floor then i can only build 20 sq mt on the second floor Because the Total built floor space in this case should not exceed 100 sq mt.
sililarly if FSI for that same plot of land was 2 then i could build 2×100 = 200 sq mt on my plot of land.