I’m not sure what context that link is assuming, but in an analysis context I typically see little o used in ways like e.g. “f(x)=f(x0)+dfdx|x0dx+o(dx2)”. The interpretation is that, as dx goes to 0, the o(dx2) terms all fall to zero at least quadratically (i.e. there is some C such that Cdx2 upper bounds the o(dx2) term once dx is sufficiently small). Usually I see engineers and physicists using this sort of notation when taking linear or quadratic approximations, e.g. for designing numerical algorithms.
I’m not sure what context that link is assuming, but in an analysis context I typically see little o used in ways like e.g. “f(x)=f(x0)+dfdx|x0dx+o(dx2)”. The interpretation is that, as dx goes to 0, the o(dx2) terms all fall to zero at least quadratically (i.e. there is some C such that Cdx2 upper bounds the o(dx2) term once dx is sufficiently small). Usually I see engineers and physicists using this sort of notation when taking linear or quadratic approximations, e.g. for designing numerical algorithms.