Microbiota
This is the community of living microorganisms (bacteria, fungi, etc.) residing in a defined ecological niche. This can be the human body or individual parts of the body, such as the skin, the oral cavity, or the digestive tract.

Microbiome
This is the set of microorganisms, their genes, and their metabolites (enzymes, lipids, polysaccharides, etc.) that make up a well-defined ecological niche and have distinctive physicochemical properties.

Prebiotics
Compounds that stimulate the growth or activity of native microorganisms, resulting in an intended cosmetic benefit. Structurally, they are oligo- or polysaccharides, mainly formed by the polymerisation of fructose, galactose and mannose polymers, or mixed compounds.

Probiotics
They are viable, active (growing) or latent (non-growing, but metabolically active) microorganisms that, when administered in adequate (very high) amounts, confer an intended cosmetic benefit, either directly or through an effect on the host's microbiome. Microbiological limitations on finished cosmetics (ISO 17516) significantly hamper their use.

Postbiotics
A preparation of inanimate microorganisms and/or their components that confers an intended cosmetic benefit. These components may be cells or cell fractions, a fermentation filtrate, or a metabolic product or byproduct secreted by living bacteria or released after bacterial lysis. This category absorbed the former category of parabiotics.

Genus
A group of organisms that have one or more common traits. It is a taxonomic category that falls between a family and a species.

Species
A group of similar organisms within a genus. They are designated by biochemical and other phenotypic criteria, and by DNA similarity, which groups strains based on their overall genetic similarity.

Strain
In microbiology, a population of microorganisms of a single species descended from a single cell or originating from a specific sample, which is usually clonally propagated due to the interest in preserving its defining qualities.