Stripped off any Hindu background it is just a meaningless word or syllable which can help you relax very deeply.
Mantra meditation is a very easy to learn and effective relaxation technique.
Just thinking a mantra helps you focus your attention on the inside and eventually reach a state of very deep rest. Regular practice of meditation reduces ones irritability and thus the feeling of being stressed. It also reduces the time of recovery after distressing situations. During the first weeks of practicing mantra meditation some people tend to become more sensitive. I have made a very similar course with youths who easily are filled with enthusiasm and therefore tend to overdo the exercise.