Probiotic is a popular term that is increasingly used to describe food products and dietary supplements. Not all of these things that are called "probiotics" actually are.
What is a probiotic exactly?
How do probiotics work?
Probiotics are defined by the World Health Organisation as live microorganisms that when applied in sufficient amounts confer a health benefit on the host. The probiotic definition is intentionally broad because it is intended to cover the use of probiotics on different body sites and for different health conditions. Yet, in all applications, the term probiotic should only be used to describe the presence of living microorganisms that have been proven to result in a health benefit.
Those microorganisms should be defined at the strain level and have genome sequences which are known.
When considering a probiotic, you want to know that you can look at the research for that particular strain. Not all strains have the same function or action in the body.