The article revisits the definition of the microbiome, addressing the rapid evolution and growing interest in microbiome research. It highlights the lack of a clear, commonly agreed-upon definition and best practices in the field. The authors, who participated in the MicrobiomeSupport project, propose a revised definition based on Whipp et al.'s 1988 work, incorporating recent technological advancements and research findings. They distinguish between the microbiome and microbiota, emphasizing the importance of considering the composition, heterogeneity, dynamics, stability, and resilience of microbial networks. The article also discusses core microbiomes, keystone species, and co-evolutionary principles within the microbiome. It aims to improve standardization in microbiome studies and facilitate the transfer of knowledge from basic science to practical applications, particularly in addressing anthropogenic-driven changes in planetary health. The historical development of microbial research is reviewed, and the challenges and gaps in current definitions are discussed, leading to recommendations for a more comprehensive and unified conceptual framework.The article revisits the definition of the microbiome, addressing the rapid evolution and growing interest in microbiome research. It highlights the lack of a clear, commonly agreed-upon definition and best practices in the field. The authors, who participated in the MicrobiomeSupport project, propose a revised definition based on Whipp et al.'s 1988 work, incorporating recent technological advancements and research findings. They distinguish between the microbiome and microbiota, emphasizing the importance of considering the composition, heterogeneity, dynamics, stability, and resilience of microbial networks. The article also discusses core microbiomes, keystone species, and co-evolutionary principles within the microbiome. It aims to improve standardization in microbiome studies and facilitate the transfer of knowledge from basic science to practical applications, particularly in addressing anthropogenic-driven changes in planetary health. The historical development of microbial research is reviewed, and the challenges and gaps in current definitions are discussed, leading to recommendations for a more comprehensive and unified conceptual framework.