What is Self-Sovereign Identity (SSI)?
Self-Sovereign Identity, as a standalone phrase (or acronym), is a very confusing, overloaded, ambiguous term whose use should be avoided in all situations. In conversation, an article, or a standards document, it could mean any of the uncontracted terms in the following figure. The term Self-Sovereign Identity (or its acronym SSI) could refer to any or all of the uncontracted terms in the following figure – unless an author has taken care to be clear and precise with respect to every occurrence of the term and/or its acronym.
 The most recent example of SSI confusion is the Principles of SSI document published by the Sovrin Foundation (https://sovrin.org/principles-of-ssi/). The document makes no attempt to define SSI nor state what SSI is intended to be an acronym for. Princples of SSI has resulted in a lot of confudsion (https://hyperonomy.com/2018/12/18/definition-confuding/) in the decentralized identifer communities as different working groups try to apply the Principles in new domains without for descerning: a) precisely which definition/application of SSI should be used and b) the types or categories of principles being represented in the document. Without first having a clear and precise definition for (a), successfully achieving (b) is almost impossible.