Synbiotics
Products combining live microbes with a substrate that feeds them.
A synbiotic is a product combining probiotics, live microorganisms, with prebiotics, the substrates those or other microbes feed on. The intent is to supply both the organism and its food together.
The category is defined more carefully than the marketing suggests. The international scientific association that maintains these definitions distinguishes complementary synbiotics, where each component works independently on its own evidence, from synergistic synbiotics, where the prebiotic is specifically selected to be used by the co-administered organism.
That distinction is where most commercial products fall down. Combining any probiotic with any fibre and calling it synbiotic meets the label and not the concept, and the evidence for the combination is rarely tested as a combination.
The underlying rationale is reasonable. A swallowed organism has to survive the journey and find something to eat in a colony that is already established, so arriving with its own substrate is not a silly idea.
The evidence base is thinner than for either component separately, and both of those are narrower than their marketing. Probiotic effects are strain and condition specific; prebiotic evidence largely reduces to the case for fibre; and the combination has been tested mainly in specific clinical settings rather than for general wellness.
There is a food version that costs less and has better evidence: fermented foods eaten alongside a high fibre diet, which is a synbiotic pattern in everything but branding.
In practice, unless you have a specific condition and a specific product with evidence for it, spend the money on fibre and fermented food rather than on a combination capsule.