It means three things - the title of a movie, the name of the village Buddha that sets in motion the plot of the movie, and the sound that an elbow makes when applied with vigor to the very tippy-top of someone's head.
It is clear to me that Ong Bak is a complicated metaphor for the Eightfold Noble Path of enlightenment.
The Way to the End of Suffering: Buddha teaches that the Middle Way is the right way to the end of suffering. Ong Bak teaches that a flying elbow to the nugget will promptly end suffering.
Right View: Buddha teaches that we must train our perception to attain Nirvana. Ong Bak, on the other hand, teaches that the right view is that of the crown of your opponent's head, as you crash down upon it with a thundering elbow.
Right Intention Buddha teaches us that our aspirations are as important as our outcomes. Ong Bak teaches us that one can not administer a crushing elbow to the nugget unless one intends to do so.
Right Speech The Buddha teaches that words must be kind, necessary, and true. Ong Bak teaches us that words mean little, especially in the confusing, dishonest city. Say little, do much. Those who break their word (particularly in regards to any sort of Buddha-head) will eventually be crushed by a gigantic Buddha-head. One should avoid this.
Right Action Buddha teaches us that, having set out to end suffering, cultivated sublime perception, formulated a compassionate intent and spoken with compassion and truth - one must then also DO the right thing. Ong Bak teaches us that the right action is either an elbow to the top of the head, or any sequence of events that leads to same.
Right Livelihood The Buddha teaches us that our means of self-sustenance must not be at the expense of others - that we ought to contribute to the community rather than detract from it. Ong Bak teaches us that fighting is never right, unless it is for the sake of the Buddha's head, or to save a girl. One must not profit from fighting, no matter how many people are trying to shove bhat into your hand for doing it.
Right Effort The Buddha teaches that effort is different from action and intent - that one can intend to do good, and do good acts - but expend effort either fruitlessly or at counter-purposes. One must then expend effort in achieving good aims. Ong Bak teaches us that Right Effort includes never leaping over things in a simple manner, but instead, always either feet-first or with a full (or preferably double) flip. A simple punch to the face is insufficent, one must clonk the top of the head with a flying elbow. The simple and pragmatic is useless to Ong Bak - the fancy and ostentatious is the only appropriate way.
Right Mindfulness The Buddha teaches that we must be vigilant and sure that our own thoughts are always compassionate - we must practice mindfulness. Ong Bak teaches us that those who are mired in an unmindful way of living, who are caught in the trap-of-the-world can be freed from their imprisonment by a jarring blow to the Crown Chakra. Probably with a flying elbow - though sticks, rocks, and gigantic stone Buddha-heads will also do the trick.
Right Concentration The Buddha teaches that meditative concentration will release the mind from its cage (the body) and allow it to perceive the perfection to which all humans are inherently born. Ong Bak teaches that the greedy, selfish, or evil can be jarred from their fallen state and lack of compassion by a... well, you can probably guess at this point.
The Development of Wisdom The Buddha teaches that wisdom will not come accidentally - but rather from a purpose-filled life following the Path. It must be apprehended directly, not taught. Ong Bak teaches us that wisdom comes from having the capacity to administer a flying elbow to the head at any moment, but largely refraining from doing so. Also, sometimes wisdom comes from being crushed to death by a gigantic stone Buddha-head.
As you can see, Ong Bak is a beautiful testament to Buddhist thought and teaching.