In C#, value types are data types that directly contain their data, while reference types are data types that store a reference to the memory location where the data is stored.

Value types include simple types such as integers, floating-point numbers, and enums, as well as composite types such as structures and tuples. When a value type is assigned to a variable, a copy of the value is made and stored in the memory location designated for that variable.

Reference types, on the other hand, include objects, arrays, and strings. When a reference type is assigned to a variable, a reference to the memory location where the data is stored is created, rather than a copy of the data itself. This means that changes to the data made through one variable are reflected in all other variables that reference the same memory location.

In summary, the key difference between value types and reference types is that value types directly contain their data, while reference types store a reference to the memory location where the data is stored.