Representation of the People Act, 1951 is the Act and law that leads, defines and guides the elections in India to the Parliament and to the state legislatures.
'Office of profit' comes under 'Constitutional disqualifications' as per Article 102(2) of Indian Constitution. That does not say specifically define 'office of profit'.
However the (PREVENTION OF DISQUALIFICATION) ACT, 1959 (10 OF 1959) lays down a number of offices which are exempted from the disqualification under office of profit.
There are many exemptions of posts of profit, with subsequent amendments and similar acts in states. Thus it makes it a sort of discriminatory. It is in this context that there is a debate going on to totally remove the reference of office of profit as a disqualification. The original purpose was to prevent people holding responsible posts earning from government and who can influence voters by the posts they hold. Today, with much political awareness among people about their rights and duties, voters may not get influenced by posts and designations.