The Controller Area Network (frequently stylized as CANBUS, or just CAN) is an internationally standardized networking protocol, used by modules in modern automobiles and industrial vehicles (tractors, forklifts, etc).
.dbc formatNodes communicate with each other in a way that is, for the most part, unreadable and otherwise useless to humans in its raw form. Therefore, a semi-standardized format was developed by Vector GmbH to facilitate interpreting and translating the raw Signal values (from sensors and modules), into human-readable values and units (for gauges and data-loggers).
This is the .dbc format I'll be focusing on in this Wiki and its accompanying canbus repository.
Every auto manufacturer has their own proprietary "dictionary" which contains the mappings of their platform's specific adjustment factors/offsets, labels, and units, used to translate the raw sensor values into meaningful data points.
Sometimes these dictionaries ("databases" or "documents" ) are leaked online (or sold by a disgruntled former employee). In most cases, however, its due to enthusiasts such as myself spending countless hours, usually in their own personal vehicles, painstakingly reverse-engineering translations for individual signals to assemble a .dbc file.