Synbiotics are defined as mixtures of probiotics (substances containing live cultures of beneficial microbes) and prebiotics (fibres that act as food for these bacteria) that support gut health.
Swanson KS, Gibson GR, Hutkins R, et al. The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of synbiotics. Nat Rev Gastroenterol Hepatol. 2020;17(11):687-701. doi:10.1038/s41575-020-0344-2