In statically-typed languages, there are two different, often confused, concepts when discussing the top type.
In dynamically-typed languages, the second concept does not exist (any value can be assigned to any variable anyway), so only the first (class hierarchy) is discussed.
Any OCaml object can be explicitly upcasted to this type, although the result would be of no use.
The notion of top is also found in propositional calculus, corresponding to a formula which is true in every possible interpretation.
In description logic, top is used to refer to the set of all concepts.
(the bottom type or empty set corresponds to owl:Nothing).