>>13126365EI is the flexural rigidity and tells you how resistant a structural member is to bending.
E is the Young's modulus and defines stiffness due to material properties.
I is the second moment of area and defines stiffness due to geometry (imagine a ruler when it is flat, very easy to bend, but when you turn on its side it becomes extremely difficult to bend. Its second moment of area is higher on its side).
