Question

define population and its various forms?

Answer 1

Hello !!
here is yor anser 
In biology, a population is all the organisms of the same group or species, which live in a particular geographical area, and have the capability of interbreeding.[1][2] The area that is used to define a sexual population is defined as the area where inter-breeding is potentially possible between any pair within the area, and where the probability of interbreeding is greater than the probability of cross-breeding with individuals from other areas.In sociology, population refers to a collection of humans. Demography is a social sciencewhich entails the statistical study of human populations. Population in simpler terms is the number of people in a city or town, region, country or world; population is usually determined by a process called census (a process of collecting, analyzing, compiling and publishing data)

This article refers mainly to human population.
hope it will help you

Answer 2

population refers to the increase the number of inhabitants of a country during a specific period of time.
it various forms are :-
1) birth and death rate
2) migration
3) age composition