The object pool pattern is about re-using objects by putting back wasted objects into the pool (perhaps up to an upper limit) instead of deleting them. So sub-sequent allocations are fed from the pool until those is depleted. The pool may be preset with a minimum of objects.
The pool allocation scheme is a concept where (usually fixed size) objects are allocated from a pre-allocated block of memory. Its purpose is to avoid the costs of generic new/delete or malloc/free operations in situations where the memory usage pattern is known.
Both concepts are independent; they can even be combined.