An original genealogical record or source is one that is just that – original. It was not copied from another record, and is considered the most reliable.
A derivative source is one that was copied from another record. This might be by transcription by hand or machine, photocopies, microfilm, or abstracts. The more layers of copying between a derivative record and the original, the more potential for problems
Because every repetition or recopying of data is an opportunity for error, the closer the derivative is to the original the more reliable the data are likely to be