Both M.tech and m.s is postgraduate degree. Generally b.tech and m.tech terms are used in indian institute or some Asian institute in most of the country you will find bachelor of science (b.s) and Master of science (m.s) . the main difference which i found in m.tech and m.s is research . m.s is a research oriented term and m.tech is more of a professional term .
M.S is research oriented course whereas m.tech is job oriented ( there are people who do research during m.tech but most of them are job oriented) but in foreign nations they see education as a tool for upliftment and betterment of society rather than joining a course just sake of getting high package salary.
M.s is a degree under science discipline whereas m.tech is a degree under engineering discipline.
Most of the student join b.tech just because of salary which are shown by media this is a harsh reality.
There's nothing special about using m.s and m.tech terms because some institute in india offers both m.s and m.tech course like
1. IIIT HYDERABAD
hope this will help you