Slow slip is one of the mechanisms of relaxation of tectonic stresses in the Earth's crust. It has been recorded in seismically active zones over the Earth, and it is accompanied by low-frequency and very low-frequency earthquakes. The paper presents modern concept about the physics of slow slip and examines the spatiotemporal linking slow slip and ordinary earthquakes. The discovery of slow slip phenomenon has revolutionized our understanding of the physics of deformation processes occurring in the Earth's crust and motivates us to develop a two-stage model of earthquake nucleation – initiation at the first stage of slow slip, which at the second stage transforms into rapid rupture.