Sampling is the process of selecting a small portion from a bulk material for analysis. A sample is this chosen portion representing the bulk material or population.

The material can be of different types - solid, liquid, or gas, whose composition can be either homogeneous or heterogeneous.

For a homogeneous material, a single sample drawn, referred to as the grab sample, is sufficient for analysis.

However, for heterogeneous material, several incremental samples are selected from the different parts of the bulk material and combined for analysis. This is known as the gross sample.

A homogeneous subset of the gross sample suitable for laboratory analysis is called a laboratory sample. A part of the laboratory sample that is analyzed is denominated as an analysis sample.

The different sampling methods are random, judgemental, systematic, stratified, and cluster sampling.