F# uses the CLR term "value types" instead, or sometimes "struct" types as in the C# keyword.

These are usually defined with the [<Struct>] attribute over a regular type definition, or using the struct keyword before tuple/anonymous record types. Also, the original 'T option type now has a value-type successor 'T voption.

In .NET the unboxed types are value types and boxed types are reference types. And you can box and unbox them.