One Rank One Pension (OROP) is a pension reforms movement for Indian armed forces personnel. To understand this let me briefly explain how pensions for government employees work in India.
My dad retired last month from a government bank. His pension is 50% of the salary he drew at the end of last month. This pension is then increased every year to account for inflation. When my dad's junior employee retires 10 years from now, he would likely draw a far higher pension than my dad because the salary at the end of his service might be higher and the pension is 50% of that salary. [Salaries can grow a lot faster than inflation in the government.] This can be a bit unfair as both my dad and that person would have served the same number of years at the bank and at the same rank.
This issue can be far more critical in the armed forces where rank and prestige matters a lot. A General who retired in 1980 after 30 years of service might be drawing far less pension than a Major who retired in 2015 after 20 years of service. The General served the country longer and at a higher rank. Why should he receive a lower pension just because he retired in 1980?
One Rank, One Pension reform would allow the General who retired in 1980 receive the same pension as a General retiring in 2015 serving the same number of years in the army. This is especially needed in the military where soldiers retire far younger and could neither easily switch to other careers nor get a living wage from the pension.
So far so good. What is the glitch? In fact, the OROP existed until 1973. The glitch is that it requires a lot of money [Rs 8300 crores/year and upwards]. For every pay increase to the existing forces, all past pensioners also have to get a rise. As Indians live longer this means the government has to pay pensions to each person for decades and at rates fast increasing. And more. When it is implemented for the military, the other government employees, starting from the paramilitary, are also going to ask for it. Given that it involves a few thousand crores, every government is dragging its foot.