By combinators they mean things like folding/reducing over lists, i.e. combinators/higher order functions for operating on potentially infinite structures. It'

By combinators they mean things like folding/reducing over lists, i.e. combinators/higher order functions for operating on potentially infinite structures. It's not as expressive as raw recursion since many uses of recursion are hard to express through combinators, albeit a great deal of research has been done in this area (look up recursion schemes).