What do you mean by retrospective and prospective effect in legal sense?

In Indian Lwa “A new law ought to be prospective, not retrospective in its operation.” The meaning of the word prospective with reference to statutes shows that it is concerned with or applying the laws in future or atleast from the date of commencement of the statute. Whereas the word retrospective when used with reference to an enactment may mean: 1. Effecting an existing contract or 2. Reopening of the past , closed and completed transactions, or 3. Affecting accrued rights and remedies, or 4. Affecting procedure.

RETROSPECTIVE

 

Looking backwards.

This word is usually applied to those acts of the legislature, which are made to operate upon some subject, contract or crime which existed before the passage of the acts, and they are therefore called retrorospective laws. These laws are generally unjust and are, to a certain extent, forbidden by that article in the Constitution of the United States, which prohibits the passage of ex post facto laws or laws impairing contracts.

PROSPECTIVE:

Looking forward; contemplating the future. A law is said to be prospective (as opposed to retrospective) when it is applicable only to cases which shall arise after its enactment.

 

 

According to google answer, 

Retrospective: Looking back on or dealing with past events or situations

Eg: The Government introduced retrospective legislation to change the rules

Prospective: Expected or Expecting to be the specified thing in the future.

Eg: A meeting to discuss prospective changes in government legislation.

but I learn :)

Reterospective => In law,,, it means that the present law or act cant be apply on the previous offences . like a person got punishment of 2 years for some offence then after some mounths a new law come and the offence punishment is of 4 year in this case the person is entitled only for 2 year punishment not for 4 years 

In general if there is no mention of prospective or retrospective than it is Prospective by default. For Retrospective it should be explicitly mention in the Act.

Prospective is simply taking effect or applicability hence forth, whereas the Retrospective is past as well, therefore retrospective has got lot of dependencies and effects the rights or may deprive as well or create liability which was already relaxed or exempted. My 2 cents. Thanks.