Cost Discount

A Cost Discount X allows you to modify one number that is expressed as a digit on the cost text by X.

So for example, if a cost were to say:

And you have Cost Discount 1; you can change any of the 2s in the cost text to a 1 (or a 3). You CANNOT change the any three costs part, because that is not written in numerical form.

Another example: if a cost says "Sac 1 creature", you can bring that down to zero; but if it says "Sac a creature", you cannot.

The most traditional way to get a Cost Discount is through the process of Hidden Knowledge; however there are cards that can give you a Cost Discount as well.