Table 1.

Microbiome and metabolome glossary.

Term	Definition
Psychoneurological symptoms	Symptoms that often co-occur and have similar potential underlying causal pathways. Examples include pain, fatigue, sleep disturbance, anxiety, depressive symptoms, and cognitive dysfunction.
Microbiome	A community of microorganisms (bacteria, viruses, and fungi) that reside in different parts of the human body, such as the skin, gastrointestinal tract, oral cavity, and vagina.
Microbial composition	A description of the microorganisms that form the microbiome. Compositional components include microbial abundance and diversity metrics (alpha and beta diversity).
Microbial abundance	The quantity or proportion (relative abundance) of a specific microorganism that resides in the microbiome.
Alpha diversity	Measurement of microbial species diversity within a given sample or microbial site.
Beta diversity	Measurement of dissimilarity (or similarity) of species diversity between two or more samples or microbial sites.
Metabolome	The collection of small molecules (metabolites) and their interactions within a specific biological system or sample.
Metabolites	Small molecules that are substrates, intermediates, or products of metabolic reactions that regulate various physiological functions within a cell or organism.
Untargeted metabolomics	An analytical approach that aims to comprehensively detect and quantify metabolites within a sample due to limited prior knowledge; often used as an exploratory tool.
Targeted metabolomics	An analytical approach that aims to quantify specific types of metabolites within a sample based on known relevant metabolic pathways or physiological processes.
Metabolomic pathway	A sequence of chemical reactions that produce new molecules (synthesis) or breakdown complex molecules (degradation).