Microbiome: the ecological community of commensal, symbiotic, and pathogenic microorganisms that literally share our body space.

Metagenome: all the genetic material present in an environmental sample, consisting of the genomes of many individual organisms.

Metagenomic sequencing: the high-throughput sequencing of metagenome using next-generation sequencing technology.

Metagenomics: the study of genetic material or the variation of species recovered directly from environmental samples.

Descriptive metagenomics: estimation of microbial relative abundance based on different physiological and environmental conditions to reveal community structure and variation of the microbiome.

Functional metagenomics: the study of host–microbe and microbe–microbe interactions toward a predictive dynamic ecosystem model to reflect a connection between the identity of a microbe or a community.