Definition:
Canonical data models are a kind {of data|of knowledge|of information} model that aims to present data entities and relationships in the simplest possible form in order to integrate processes across various systems and databases. more often than not, the data exchanged across various systems rely on different languages, syntax, and protocols. A CDM is additionally called a common data model.
Further Reading:
Book: Agile Testing by Janet Gregory and Lisa Crispin.