These terms come from the world of management information, data warehousing and data quality.

[Accuracy][1] is easy:

First, it has to be or the right value. Second, it has to precisely represent the value in consistent form in accordance with the business data model and architecture.

[Believability][2] is harder. It consists of the quality of the source and the quality of the processing, also called (data) provenance or lineage.

As with accuracy definitions in the field differ, a nice one is:

“the extent to which data are accepted or regarded as true, real and credible”

Be assured that data quality has lots more dimensions. Some references:
https://en.wikipedia.org/wiki/Data_quality
http://www.learn.geekinterview.com/data-warehouse/data-quality/what-is-data-accuracy.html
http://web.mit.edu/smadnick/www/wp/2007-11.pdf
[1]: https://en.wikipedia.org/wiki/Data_quality [2]: http://web.mit.edu/smadnick/www/wp/2007-11.pdf

These terms come from the world of management information, data warehousing and data quality.

Accuracy is easy:

First, it has to be or the right value. Second, it has to precisely represent the value in consistent form in accordance with the business data model and architecture.

Believability is harder. It consists of the quality of the source and the quality of the processing, also called (data) provenance or lineage.

As with accuracy definitions in the field differ, a nice one is:

“the extent to which data are accepted or regarded as true, real and credible”

Be assured that data quality has lots more dimensions. Some references:
https://en.wikipedia.org/wiki/Data_quality
http://www.learn.geekinterview.com/data-warehouse/data-quality/what-is-data-accuracy.html
http://web.mit.edu/smadnick/www/wp/2007-11.pdf