A membrane that is not rigid in the plane, or has zero in‐plane shear modulus, is said to be fluid; one that does have a nonzero shear modulus in the plane is said to be solid‐like. A fluid membrane shaped, say, like a rectangle will be easily deformed when antiparallel forces are applied along two of its parallel edges. In many cases the interesting excitations, or conformations, of a fluid membrane arise from out‐of‐plane bending.