In a pharmaceutical context, Off-Label refers to uses of drugs that are not approved by the regulators and cannot therefore be printed on the product label or officially promoted by the drug company. More generally, it refers to any unauthorized or emergent use of a product or service.
From the regulatory point of view, off-label is not merely unapproved but (at least to some extent) disapproved, and subject to secondary regulation.
Off-Label Drug Use: What You Need to Know (WebMD, undated)
But off-label usage is apparently increasing. This raises several questions, which are raised in separate blog postings.
Off-Label as Innovation (March 2005) - the technological leading edge is often/always off the label.
Off-Label Trust (March 2005) - on-label and off-label usage rely on different trust mechanisms.
Off-Label as Samizdat (March 2005) - off-label usage is disseminated by informal knowledge mechanisms
SOA Pharma (March 2005) - there is a critical asymmetry between on-label and off-label, which must be accommodated in the geometry of services
Off-Label Dog Whistles (March 2005) - in a political context, dog-whistle refers to uses of issues that are not approved of in terms of civilized politics and cannot therefore be printed in the manifesto or officially promoted by a serious party. (Guest post by John).
See also On Repurposing AI (November 2018)
Links corrected 3 November 2018