The word humiliation comes from a Latin root meaning earth. To humiliate someone is to bring him or her down low to the ground.
Humiliation is a highly subjective issue, and depends greatly on context. Although there are many examples of humiliation as a technique, success in training all depends upon the slave and what they find personally to be most degrading. While in a dominant-submissive scene or relationship, the submissive takes a subordinate role and may be called "slave", "boy", "dog" or something similar. The submissive may also make displays of subservience, such as lighting cigarettes, walking a pace behind the dominant, only speaking when spoken to, etc.
Humiliation play can involve physical and/or verbal methods. Some seek to be demeaned by acting a role, while others enjoy to be 'tonguelashed' and to be constantly told of their low status, and even be made to repeat this back to the humiliator. One example may be as simple as having a slave call their Master "Sir" or "Master." For some, this in and of itself is utterly humiliating, while other slaves may find that is not humiliating whatsoever. On the flip side, having a slave wear a collar and perform submissive acts in public or within the confines of a scene with other people may seem humiliating to some, but normal and natural to others.
However, a dominant may take care over insulting the submissive. Terms like "fat", "ugly", "stupid" or "worthless" could be considered abuse if this is not part of the understanding the top and bottom have negotiated for their role play scene.
Depending on the roles and persons involved, terms like "slut", "tart", "bitch" and "whore" may or may not be considered humiliation. For some people, such names are a way of achieving ego reduction, entering bottom space, or getting over sexual inhibitions.
A classic technique to put a submissive into bottom space is to combine humiliation with pleasurable physical sensation, including sexual stimulation. Someone who is already inclined to be subby can often be put into a very submissive mental state by simultaneously turning that person on physically while humiliating them.
Sexual roleplaying may or may not involve humiliation. For example, one bottom who plays the part of a dog may enjoy being mock-forced into it and the top will emphasize the lowness of the bottom's status as an animal. Another dog-player would rather play the role of the dog without any element of humiliation.
One such form of sexual roleplaying is objectification, where the bottom is cast in the role of an object.
It is also widely accepted that there are individuals who seek humiliation as a form of emotional release, thus, doing things like eating out of a dog dish, being forced to always kneel, displaying oneself or being forced to cross dress, are just methods a Master can use to bring their slave that much wanted emotional release.