In comparison to other epistemic sources (perception, memory and reason) testimony is the only one dealing with the social aspects of gaining and justifying knowledge. One main problem of the current discussion about knowledge by testimony is the concept of testimony itself. It is quite unclear what the correct notion of testimony is supposed to be. In this essay I present a proposal to define the concept of testimony in making a distinction between the conditions which hold in the speaker's context and the ones necessary and sufficient for the hearer. Furthermore, I will briefly defend the thesis that there is not one general concept of testimony, but that there are different ones connected via a kind of specialisation relation.