Question

A portion of the population selected to represent the population is called

Answer 1

A portion of the population selected to represent the population is called sampling. It has two advantages, i.e. it is faster and less costlier as the rate involved in taking data from entire population turns out to be a costly affair. 

Answer 2

A portion of the population selected to represent the population is called a "sample". Once samples are collected, statistics are calculated and inferences are made. 
The disadvantages of such a method are:
1. Inferences may be biased and not representative of the community and hence may lead to wrong conclusions. 
2. Inadequate knowledge - Researcher may lack, lacks expert knowledge in sampling and can commit serious mistakes, resulting in misleading results.