This is a question which many of us are confused about. I asked a lot of people about this, but could not find a satisfactory answer. Even I found this question to be a little hard for 'Google' to answer.
So, this is what I came to learn after spending some time googling. Here is it for you...
In India, Gazette is published on regular basis, it is an official Central Government Publication. Among many other things (viz. GoI notifications, rules, orders etc.), it publishes the promotions & transfers of certain government officials (who are called Gazetted Officers). This practice is followed since British times; and that publication is called by the Government of India as the "Gazzette of India".
Any catagory of persons who are listed in "Gazette of India" are Gezetted. As simple as that..!!
Governments categorise their employees from Class 1 to 4.
Class 4: Unskilled or semiskilled.
eg. Peon, attender, driver, gardener, Lans Naik, Naik etc
Class 3: Semi skilled with no decision making authority.
eg. Clerk, Head clerk, Assistant, Typist, Stenographer, Telephone operator, Havaldar, Havaldar major and NCOs, etc
Class2: Officers with some supervisory/managerial role.
eg. Section Officer, BDO, Tahsildar, Junior doctors, Assistant Executive Engineer, Lecturers in Government colleges, Headmaster of Government high schools, Junior Doctors in Government hospitals, 2nd Lieutenant to Major, etc
Class 1: Executive power vested officers,with decision making powers.
All India services, though posted to states; promotees from states to the cadre of Assistant Commissioner and above and to the cadre of All India services ; Police officers of Circle Inspector and above; Additional District Civil surgeons, Executive Engineers and above, District Medical Officer and above, Lt.Col. and above, Principals of Government colleges and above, Readers and above of Universities, etc.
Nationalised bank officials are not gazetted officers but protocol ranks exist.
Among the powers and responsibilities of a Gazetted Officer, are the certifications and authentification of photo copies etc. That's why we go to them for attesting our copies where they actually have to see an original of that and certify that the copy is the actual copy of the original as seen by them.