Step 1: Start with the given differential equation.
The given differential equation is
\[
\frac{d^3y}{dx^3}=0.
\]
This means the third derivative of \(y\) with respect to \(x\) is zero.
Step 2: Integrate the differential equation.
Integrating once,
\[
\frac{d^2y}{dx^2}=C_1.
\]
Integrating again,
\[
\frac{dy}{dx}=C_1x+C_2.
\]
Integrating one more time,
\[
y=\frac{C_1x^2}{2}+C_2x+C_3.
\]
Step 3: Compare with the given expression.
The obtained solution can be written as
\[
y=ax^2+bx+c,
\]
where \(a,b,c\) are arbitrary constants.
Since the third-order differential equation has three arbitrary constants, this represents the general solution.
Step 4: Final conclusion.
Therefore,
\[
\boxed{\text{the general solution}}
\]