This is a draft of an upcoming report from UNESCO; as of right now it does not appear to have a permanent URL. Note that it's a discussion paper, not a definition endorsed by UNESCO. "This preliminary report proposes a definition arrived at through a consensus-building process by a global expert panel." Here's the proposal (quoted):
A micro-credential: 1. is a record of focused learning achievement verifying what the learner knows, understands or can do; 2. includes assessment based on clearly defined standards and is awarded by a trusted provider; 3. has stand-alone value and may also contribute to or complement other micro-credentials or macro-credentials, including through recognition of prior learning; and 4. meets the standards required by relevant quality assurance.
What follows is less a defense of the current statement and more an engaging discussion of some of the issues surrounding micro-credentials (for example, the credibility of providers, and the risk of diverting funding away from established programs), an overview of the process of drafting the definition, and an outline of places where consensus was not achieved. I personally prefer version 1 (and note with dismay that the provision microcredentials are "owned, portable and sharable by the learner" was dropped by the panel almost immediately). Related: national and international reports on micro-credentials.