What is meant by delimitation of constituencies ? Why is it necessary ?

Answer:

Delimitation means fixing the boundaries of the constituencies from which representatives are elected to the Lok Sabha and the State Legislative Assemblies. It is done by a Delimitation Commission, working with the Election Commission, mainly on the basis of population figures of the census.

It is necessary because population changes with time. Delimitation keeps the population of each constituency nearly equal, so that every vote has about the same value, and it also decides which constituencies are reserved for Scheduled Castes and Scheduled Tribes.