Let \(X \to k\) be a scheme over a field \(k\). An infinitesmal deformation of \(X\) is a scheme \((X', \mathcal O_X')\) flat over \(D = \Spec k[\epsilon]/(\epsilon^2)\) such that \(X\) is isomorphic to the fiber of \(X'\to D\) over the closed point of \(D\).