How much was a crown worth?

Could you please clarify for me, what specific time period are we referring to when discussing the value of a crown? Is this in relation to historical currencies, or perhaps a digital currency system? And furthermore, are we talking about the monetary value in terms of another currency, such as gold, silver, or even modern-day currencies like the US dollar or Euro? It's important to have a clear context in order to accurately answer the question, "How much was a crown worth?