Definitions for "Credibility"
The quality of being credible; credibleness; as, the credibility of facts; the credibility of witnesses.
You're standing with the group, the degree to which they see you as sincere, competent and congruent. Establishing your credibility helps establish a positive expectation set that will increase learning for the group. Sometimes you need to disclose your qualifications as an authority on the subject.
8,9,10,11,12 The quality or state of offering reasonable grounds for being believed.
The power to have a statement accepted into the Shared Imaginary Space (or diegesis). In other words, whether what you say is "real" within the game-world. For example, a player may say "I chop his head off" -- but the statement doesn't have credibility until the GM confirms by saying "Indeed, you chop his head off." Coined by Vincent Baker (aka Lumpley) on the Forge as part of The Lumpley Principle. References: Vincent's standard rant: power, credibility, and assent Player power abuse
The measure of credence or belief which is attached to a particular body of statistical experience for rate making purposes. Generally, as the body of experience increases in volume, the corresponding credibility also increases. This term would frequently be defined in terms of specific mathematical formulas.
A measure of the statistical predictability of a group's experience.
A statistical measure of reliability of experience data, based on the size of the sample.
Keywords:  pesuasive, device, useful
credibility is a useful pesuasive device.
A researcher's ability to demonstrate that the object of a study is accurately identified and described, based on the way in which the study was conducted
Ability to deceive.