The mid-ocean ridge system is formed by tectonic plates that move away from each other at divergent boundaries.
This process is known as seafloor spreading. As tectonic plates separate along these boundaries, magma from the mantle rises to fill the gap, creating new oceanic crust.
This phenomenon is a key aspect of plate tectonics, where the Earth's lithospheric plates interact at different types of boundaries, including divergent boundaries where plates move apart.