In general, a sample is a limited quantity of something which is intended to be similar to and represent a larger amount of that thing(s). The things could be countable objects such as individual items available as units for sale, or a material not countable as individual items. Even though the word sample implies a smaller quantity taken from a larger amount, sometimes full specimens are called samples if they are taken for analysis, testing, or investigation like other samples. An act of obtaining a sample is called sampling, which can be done by a person or automatically. Samples of material can be taken or provided for testing, analysis, inspection, investigation, demonstration, or trial use. Sometimes, sampling may be continuously ongoing.
Sample characteristics 
The material may be solid, liquid, gas, material of some intermediate characteristics such as gel or sputum, tissue, organisms, or a combination of these. Even if a material sample is not countable as individual items, the quantity of the sample may still be describable in terms of its volume, mass, size, or other such dimensions. A solid sample can come in one or a few discrete pieces, or can be fragmented, granular, or powdered. A section of a rod, wire, cord, sheeting, or tubing may be considered a sample. Samples which are not a solid piece are commonly kept in a container of some sort. In the field of science, a liquid sample is sometimes called an aliquot.
See also 
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