Buttcrush

It is a particular case of crush fetishism, in this case the use of buttocks.

Without giantess fetishism
People are usually shown sitting on various objects like fruits, food or toys. In some cases cruelty reaches the point of sitting on small animals (dog or cat puppies, snails, insects), which is punished by the laws of some countries.

In the case where humans interact with humans, buttcrush may present itself as sitting on some part of the body, and if on the face, then it is called facesitting.

With giantess fetishism
The enormous size of the giantesses facilitates the task of crushing them, which is why it is common to find crushing in art. In the case of the sitting, the giantesses represented:


 * Destroying structures (buildings, houses)
 * Also crushing people (there may be gore or not, it depends on the author), from here it can be deduced that it is not possible to do a "pure" facesitting because the large size of the giantess' buttocks can cover the whole body of the person.
 * Using a planet (usually Earth) as a seat.
 * By a fall: if she falls of buttocks in the sea creating a great wave, then it is a marepoto; and if she falls on earth and causes an earthquake, then it is a terrepoto.