What is Merton jump-diffusion model?

The Merton jump-diffusion model is the jump-diffusion with normal log-jumps, $J\sim\mathcal N(\mu_J,\delta^2)$, so $\phi_J(u)=e^{iu\mu_J-\frac12\delta^2u^2}$ and $\bar k=e^{\mu_J+\frac12\delta^2}-1$. Its parameters are $(\sigma,\lambda,\mu_J,\delta)$.