What is the silver content in a silver coin? Well, that varies. The term silver coin does not pertain to any particular purity of the silver in a coin. But some purities are more common than others. And, for each coin the purity of the silver is specified by the mint that produced the coin.
When considering the coin, it is important to be very specific. In some cases, the silver content has changed over time. For such coins one must know both the kind of coin and the year. A typical case of this happening is the Canadian silver dollar.