Contrary to that definition, epsilon is actually a concept used to eliminate the ambiguity of conversion between binary and decimal representations of values. For example, 0.1 in decimal doesn’t have a simple binary representation, so when you declare a double as 0.1, it is actually setting that value to an approximate representation in binary. If you add that binary representation number to itself 10 times (mathematically), you get a number that is approximately 1.0, but not exactly. An epsilon will let you fudge the math, and say that the approximate representation of 0.1 added to itself can be considered equivalent to the approximate representation of 0.2.
This approximation that is caused by the nature of the representations is not needed for the decimal value type, which is already a decimal representation. This is why any time you need to deal with actual numbers and numbers which are themselves not approximations (i.e. money as opposed to mass), the correct floating point type to use is decimal and not double.