A rift valley is defined by Google’s define function as “a large elongated depression with steep walls formed by the downward displacement of a block of the earth’s surface between nearly parallel faults or fault systems.” This simply means that a rift valley is the valley created when two tectonic plates drift further apart while staying pretty parallel to each other. This creates that steep side of the valley, but it’s also a beautiful thing to see.
Due to them being formed as tectonic plates move, it can take a lot of time for a rift valley to fully form so that it can be recognized as a rift valley. Other than that, it’s just like any other valley: a place between two higher places.
Rift valleys are found on the ocean floor and on land. They occur where two lithospheric plates are separating. These are called divergence zones and are usually linear in shape.
When the crust is ripping apart, the land drops down between parallel faults. This rift valley is pretty well the same when it occurs on the floor of the ocean. You get the same valley effect when the plates separate.