Three words get used interchangeably in this field. They shouldn't be. Here's what each actually means.
Psychobiotics — the rigorous one
The most precisely defined term. Coined by Dinan, Stanton and Cryan (2013), originally "a live organism that, when ingested in adequate amounts, produces a health benefit in patients suffering from psychiatric illness."[1] It has a clear peer-reviewed origin and is safe to use.
Psychobiome — the useful umbrella
A broader, more informal term for the community of gut microbes (and their signalling) that influence mood, cognition and behaviour — essentially "the portion of the microbiome relevant to the mind." Popularised by a 2020 Science news feature.[2] A useful conceptual label, not a term with a single formal definition.
Neurobiotics — the emerging one
We flag this term as emerging and non-standardised. There is no single canonical peer-reviewed definition; in practice it is used loosely to mean microbiome-targeted agents intended to act on the nervous system, overlapping heavily with the better-defined "psychobiotics." Where precision matters, prefer "psychobiotics."