“Slab pull” is the pulling force exerted by a cold, dense oceanic plate plunging into the mantle due to its own weight.
“Ridge push” the result of gravitational forces acting on young, raised oceanic lithosphere around mid-ocean ridges. This causing it to slide down the similarly raised but weaker asthenosphere and put pressure on the lithospheric material further from the ridges.
“Mantle convection” the very slow motion of the Earth's solid silicate mantle caused by convection currents carrying heat from the interior to the planet's outer surface.