Quoting here from Quantum Computation by Nielsen and Chuang :
(Gottesman–Knill theorem) Suppose a quantum computation is performed which involves only the following elements: state preparations in the computational basis, Hadamard gates, phase gates, controlled-NOT gates, Pauli gates, and measurements of observables in the Pauli group (which includes measurement in the computational basis as a special case), together with the possibility of classical control conditioned on the outcome of such measurements. Such a computation may be efficiently simulated on classical computer.
A few lines further:
Consider that interesting quantum information processing tasks like quantum teleportation (Section 1.3.7) and superdense coding can be performed using only the Hadamard gate, controlled-NOT gate, and measurements in the computational basis, and can therefore be efficiently simulated on a classical computer, by the Gottesman–Knill theorem.
Does this mean that quantum teleportation can be efficiently simulated on a classical computer? What does that mean?