Convolution (f∗g)(t)≜∫−∞∞f(τ) g(t−τ) dτ(f * g)(t) \triangleq \int_{-\infty}^{\infty} f(\tau) \, g(t - \tau) \, d\tau(f∗g)(t)≜∫−∞∞f(τ)g(t−τ)dτ this is basically if you have a function fff and ggg and you slide ggg along fff, multiply pointwise and integrate it.